im still a bit confused....When playin online, do me and a bunch of mates (or randoms) Vs the AI or can i Vs other online players???

both. Online has options for co-op, you and up to 7 friends against bots, or the competetive, which is you and up to 7 friends playing against another group of 8 players. There can be bots mixed in as well to fill the ranks.

http://www.fragworld.org/frag/brink/the-fragworld-brink-compendium.html

You can do it all. Single, coop, and multi.