FAQ how to host a friendgame
1. Go to multiplayer in civ 5, klick host. check box Private game (upper left corner)
2.choose map settings, number of citystates, etc
3. Invite friends from friendlist in steam
Now steam is another issue: shift + tb opens up steam while in civ. Klick friendlist and choose ad friend. You need to know the steamname of your friends to do this. Note that the steamname might be different from the username used ingame