To load a song from a file, click the menu in the upper-left corner of the page.
Then click the Open Song menu item.
To rewind, play, or stop the song, press one of the buttons above.
To turn the metronome on or off, click on its image above.

To play your synthesizer in Performance Mode, as opposed to recording, press the Perform tab below.

To create a song, click the menu in the upper-left corner of the page, and then click the New Song menu item.