Is ranking up just like how you get money in the game, however long you stay is however much money you get, or do you have to kill people in order to rank up?

While playing you see in top middle of screen some numbers aaaa/bbbb.. aaaa is your present points and bbbb is the score you have to attain to get rank up.

Money can get you coins but not points. You have to kill, para land, destroy enemy hangar or carrier using bomb or win game to score points.

Hope it clears your queries.