If you're listening to a song in your player, you can simply click the "Add To My Mix" button in the player.

You can also add any music that is available on Groupee by going to your own site and clicking on the Control Panel link in the upper right corner. Then, click on Music on the left side bar. You'll see a list of all songs currently available on Groupee.

Clicking on a song's title it to your streaming player mix. You can then drag and drop the songs to re-arrange them.