http://www.freeciv.org/

Part of the reason it's so great is the android port.

Yeah that's fair, there is probably an overwhelming amount of features for new players. Personally I play it casually so I just experimented with each thing slightly until I got the hang of it. Against AIs it's fine to ignore things I'd say; when I started playing with friends though they started explaining the more complicated things like science bombing, why to go for cultural victories, etc.