Welcome.
Yes there is a multiplayer battles (custom battles) just like TW games, not sure how many can particpate, but its sure not less than 4 players, plus you can make an AI your ally also, custom battles, there are different maps just like TW, plus there is a map generator, which is something new.
As Mr. Graham indicated you wheather you get XIII century or Real Warfare you can play multiplayer with any other person who has any of those games (Just you need to download the latest patch for any).
For now most of time you wont find anyone in the lobby, but you can always find people ready for challenge in Xfire group, visit & join:
http://www.xfire.com/communities/realwarfare1242/
The game is much more difficult than TW games, and need some patiency, any small mistake can lead to certain defeat, but this is what I like about the game its much more realistic, and focus on tactics and early planning.
I will post some screeny as well.
Regards