Creating the UI button is relatively simple, and can be done in numerous ways. I'm guessing that you're trying to figure out what library functionality to use to perform the operation that this button would have. This, too, varies in different ways depending on what type of Minim sound you are playing.

Please show what you have so far.

The minim examples are a good place to start. Also the buttons examples. The basic idea is as follows:

But isnt there anyway of really creating a button especifically for that ? Because i have several buttons, so this way  everytime i press one button and another, the musics stops and starts.
I wanted a button that would be there and if someone wanted to turn off the music, then it would go there and click to stop it.

http://processing.org/learning/topics/button.html

I tried to make a button, but it wouldnt work..

If we see the code perhaps we can tell why :). Any way I edited the example above, a very lazy button... take a look

I think that works for me. Thank you !!