If you bought a stall you can change it by clicking the pen icon and then there is a stall icon at the right corner, click it and scroll until you find the stall you bought (or received) then click it and then you have changed it successfully. And the point of the game is get bigger ranks and donate to other players (also to get new stalls and show off your credits to other players) sadly there often are not any players online because this game is not very popular so it kind of takes off the idea of the game since there are no one to play with