Traveling is the art of using the One Power to transport over vast distances nearly instantaneously through a portal called Gateway. Traveling is also related to Skimming, which is the simplest and a little less fast way to use this kind of Weaves to open Gateways. In the world of the Wheel of Time it is considered one of the most important and useful Weaves.
Traveling was considered a lost and forgotten skill since the Breaking of the World, documented only in some ancient book. It can be guessed that it was lost because almost all the Aes Sedai knowing this Weaves died during the Breaking and also because it was impossible to use it while the world surface was reshaped continuously by the mad male channelers. Only recently it was rediscovered by both the Asha'man and Aes Sedai.
While the ability of Traveling is a Talent, accordingly to TWoTC Skimming is not, so the second can be utilized by all the channelers that know the weaves and are strong enough to open a suitable Gateway. Instead Traveling can be used only by the ones with enough strength and a minimum Talent.
Both Traveling and Skimming are usually related to the strength in One Power because only strong channelers are able alone to open suitable Gateways that are large enough to pass through. Fortunately less strong channelers can Link to each other in a Circle to provide the strength necessary to open a suitable gateway.
There are exceptions to this rule and some of the weakest channelers, such as Androl Genhald, have demonstrated the extraordinary Talent to be able to open larger and more precise gateways than other, more powerful channelers. Conversely, some stronger channelers, such as Damer Flinn, have encountered difficulty opening large Gateways and in the right position because they lack the Talent.
As stated above in the use of Traveling weaves, a minimum strength in One Power (or an extraordinary Talent) is needed to open a suitable gateway. It is unclear exactly how much power it is needed, also because the description can varies between books.
But this is in contrast to other cases, because we know lesser strong female channelers that are able to travel alone: for instance Sabeine Ocalin is a Kinswoman described as strong enough to open a suitable gateway to travel and Sabeine's level of strength in TWoTC is 21(9).
Ashmanaille Sedai, who is described using suitable gateways, in TWoTC is described with only a strength level of 22(10). But Merilille Sedai is listed with identical strength yet had to rely on the help of Reanne Corly any time she needed to travel. The same for Sibella, another Kinswoman, also at level 22(10), described as not able to open Gateways.
In such cases the strength level can be a mistake, in fact many times the levels given by "The Wheel of Time Companion" are contradictory and in some cases even clearly wrong. But observing the case of Androl it can be guessed also that sometimes a very good Traveling Talent can compensate some lacking of strength, so maybe a channeler with a good Talent at level 23(11) can open a suitable gateway and one without Talent at level 21(9) can't. Anyway considering all this cases it can be assumed with enough certainty that the minimum strength needed to open suitable gateways is around level 22(10).
Considering the examples given in the books, people with enough Talent and a strength between levels 22(10) and 17(5) are usually able to open gateway just enough for a person to pass trough. Stronger ones, with enough Talent, obviously can open larger portals, on the contrary the eventual gateways opened by people below level 22(10) aren't large enough.
Usually a pair of linked Aes Sedai each with an average strength are described to provide enough power to open a suitable gateway. An average Aes Sedai is described around a strength level of 28(16).
The books contain other strength discrepancies: in 'Lord of Chaos' Elayne (with a potential strength level described as 8+5 and almost reached) is unable to open a gateway high enough for Mat to go through while riding a horse, so he had to dismount to travel on foot pulling the horse by the reins.
Instead in 'Memory of Light' Berisha Sedai is able to open a gateway high and large enough for Faile to pass guiding from above a wagon, and Berisha is surely many strength levels below Elayne. If this is not another mistake, the explanation could be that Berisha was very talented in Traveling like Androl or that she was using an angreal or she was leading a circle (but both possibilities are truly unlikely given the description of her using of the Gateway).
Traveling is done through the use of Gateways. They initially appear as a thin vertical light line in the air, which then expands into a rectangular portal. One cannot create a gateway within a gateway. If two gateways are created to the same location, the second gateway will open beside the first, with a small gap between the two.
It is important that the channelers know their current location very well to go to another place. The Talent of Traveling seems to give to a channeler the ability to open a Gateway, the ability to “learn” through the Power the starting point, and the ability to locate the arriving point. Instead the strength is usually more related to how large a Gateway could be. But many variances and exceptions can happen.
For instance a very talented but weak as Androl can open gateways in few seconds, in vertical and horizontal position, large and short, without the need to "learn" for a while the starting point. All with a precision at the millimeter (he has showed that can cut and shape a piece of leather in his hands, using little gateways. Or open a great horizontal gateway on the floor of a room so all the people in that area fall into it). On the contrary the not very talented people, even if very strong, have difficulties to open a Gateway where it is needed, they have difficulties to locate the starting point (needing more time to "learn" it) and difficulties to open the gateway in the right position of the arriving point.
The weave holding the gateway open can then be tied off temporarily, after which the portal can be used by anybody in the area until it dissipates. If the weaves are left to dissipate, the gateway will shrink back to a single vertical light line and eventually disappear. Using the One Power, it is possible, though difficult, to stop this process after it has started. Asmodean claims that of the ancient Aes Sedai, only Demandred, Semirhage, and Lews Therin Telamon could prevent a gateway from closing.
As was described above it is very important to first memorize/"learn" the location from where you wish to open a gateway and to quicken this process a channeler can hold the source for a while.
It is later revealed there is a trick to elude the need to know very well the starting point of Traveling: in fact a channeler can create a gateway traveling to a very short distance (within eye sight, for instance) without needing to know an area. Then, once he has opened that gateway, he automatically "learns" the area well enough to make a second new gateway to go anywhere.
Male channelers describe the forming of a gateway with saidin as "boring a hole in the Pattern" to the channeler's destination. Instead, forming a gateway with saidar is done by creating a similarity in the Pattern, then stepping through the gateway to the channeler's destination.
Apparently, in the Second Age, it was customary for the user to use a sound to herald the coming of a gateway, because the edges of an opening gateway are sharp and very dangerous.
In fact opening a gateway inside an object is possible, but the edges of a gateway will slice through objects cleanly. In this respect, it can be used as a weapon, but it would likely be difficult to target a gateway to open directly into a person, in fact only people with an exceptional Traveling Talent as Androl are described as able to decapitate a Fade using this means. Recently Yukiri and other Gray Sisters developed a new way to open a gateway horizontally instead of vertically. It is revealed as useful to open this last kind of gateway far up in the sky to spy on enemies from above.
Shadowspawn cannot survive Travel through a gateway, and are killed upon passing through one. This fact was used by Lews Therin when he seized control of the One Power from Rand al'Thor when he was channeling. Lews Therin used a weave he called Deathgates, moving gateways which open and close rapidly, trapping Shadowspawn.
It is revealed by Rand that gholam were created to be able to travel through gateways. However, this ability was ultimately turned against the last known gholam when it was forced through a gateway to a void and sealed inside.
Traveling with the True Power is described as ripping a hole in the Pattern and stepping outside it entirely, and seems to be inherently destructive, possibly damaging the Pattern permanently. To Moridin's ears, 'the world screamed' as he did it. It does not use gateways; the air seems to warp and distort around users and then they simply vanish. Users of this technique can take others with them by touching them, as Hessalam did with her "pets" at Thakan'dar.