tel'aran'rhiod is the world of dreams. It is visited by many people while they dream, although most never recall their visit as anything more than a particularly vivid part of a normal dream. The landscape, structures and all other major features in tel'aran'rhiod mirror the waking world, so a building that was just painted blue would appear blue in the world of dreams as well. However, details tend to be a bit sketchier. For example, a stack of papers could be picked up and read from, and some of the information in the original stack from the waking world would appear, but not all of it.
Of course tel'aran'rhiod tends to be devoid of the people who normally inhabit the world. There are some native residents, though, and most of those are not the type that characters will be wanting to run into.
Travel in tel'aran'rhiod is much simpler than travel in the waking world. Simply concentrate on a destination, and appear there.
Any change made in the world of dreams will remain for a time (or if it is wrought with the One Power, it can be semi-permanent), but will tend to revert back to the mirror of the waking world that it was.