A web search says to find the ball at the bottom of the screen and tap it and that opens the main menu. But there is no ball at the bottom of the screen:
If I could get to the main menu, I could turn off sound, etc. (No, the thing in the lower left corner is not a menu.)
Best Answer
It looks like you've just installed the game because there are three starter Pokemon around you. Before you can access the rest of the game, you must choose to catch one of the three Pokemon.
As you can see in this video, capturing one of the starter Pokemon is an unavoidable part of the tutorial.