That AIW documentation is a very good way to get started on AIW creation and editing.
There are some nice little techniques that it doesn't mention, but it's possible to pick up along the way. There are also some minor inaccuracies (leftovers from much earlier builds I suppose), for example the left and right paths aren't auto generated anymore, you have to record those yourself.
Also it doesn't mention all the nice manual editing and fine tuning you can do on your racing paths after you've recorded them. This is very important I find, because it makes the whole process far less daunting. Some people are scared off because they think they need to drive a PERFECT lap to have a good fast path, as an example. If one or two corners aren't driven perfectly, urgh, damn, gotta do the whole lap over again. Nope, there are plenty of nice easy ways to fix those one or two corners, and also fine tune each and every corner by looking at the speed text. That'll give you a pretty immaculate path in the end.
It is also possible to create multiple paths that fit different types of cars. In one AIW you can have racing paths for GT cars, high downforce single seaters, historics, you name it. A wet path can also be created if you wish. It all depends on how much work you want to put into it.