Ello.
http://en.wikipedia.org/wiki/Airsoft
That'll help with the basic structure of airsoft. As for a lot of guys here.. weapon type and the camo they wear are usually personal preference/favour. It also depends on the playing area and what might fit in best, for example: you'd want to use shorter guns mp5/pistols etc for indoor close quarter style play and say you're playing out in the woods in summer you may want to play in something like CADPAT or US Woodland etc. So many choices and play styles.. im sure you'll get a bunch of responses.