“Heroes of Might and Magic V: Tribes of the East”

Friends, I have a rather simple question – how do I create an alliance? My friends and I want to play as a team against the AI, but we don't know how to set it up. :( I want to create a map (let's say for 4 players) and set up a 2v2 (alliance between the AI and human players). Could you please tell me where and what to set up?