Android Wi-Fi controller for Arduino robot

Hello, I'm not sure if this should be in this section, but here I go. I'm working with one friend over Arduino robot who will control a Sponge Robot. My question is how should the communication between the Andorid app and the Arduino ? I mean the Arduino is moving by stepper motors; how I should transfer the information for example "Go straight" from the app to the Arduino ? How should function like this look like ? And basically how does data transfer looks like ? I'm pretty new to this sry for dump question ?