Im very new to android dev and want to create a "pop up" when someone hits a button.

Say the button is "Get Beer"
When they hit "Get Beer" I want a pop up to say "Do you want it open when it arrives?" with 1 choice for the answer "OK"

I need to know how to 'write' the pop up code, and I also want to know how to activate it when the "Get Beer" button is pressed.