Levelshots are the images that appear when the map is being loaded in-game. Levelshots work the same on all Q3 based games (Jedi Knight 2, Quake 3, WoP etc. ) A map's levelshot must have the exact same name as it's .bsp file
.bsp files are the main map files. A map can run with no additional textures, sounds or levelshots as long as it only has a .bsp file under the maps folder in it's archive.
Q3 maps can run in WoP, but won't appear in the WoP menu. There are two ways to play them: Callvote for the chosen Q3 Map in your local server, or doing the /devmap trick. WoP uses the names of the .bsp files instead of the .pk3 archive names, so finding the map you wish to play might be tricky. /devmap also works the same way. For example, a map's .pk3 file might be called "Aster_Kitchen" but the .bsp name is AK. That would confuse regular players as they would expect Aster_Kitchen to work. Be sure to always check the .bsp file name of the map you want to play.
.bsp map files are located in the map's .pk3 archive, under the "maps" folder
.aas files are usually the bot support files for a map.