Buttons are the same as they are for computer games. You can use the mouse button down event to do whatever you want like move an actor, or make a player shoot. Please look around the forums before asking questions, some if not many of them have been answered. You should have a basic level of gameEditor before you make an app. You should at least know the events and actions, if you do this will be a lot easier for you.
There are a couple of tutorials already on touch screen buttons. Here's one of them.
http://game-editor.com/forum/viewtopic.php?f=4&t=9246&p=64348&hilit=onscreen#p64268