Put the songs on your MP3 Player
Take out the microSD card included in the MP3 Player and put it in your hard drive. You will find 7 tracks to guide you with the MP3 Player. Remove those tracks and put on your songs. But you need to name them differently (e.g. "You Are My Sunshine.mp3" must be something like "01 - You Are My Sunshine.mp3" or it can be "01-YouAreMySunshine.mp3", etc., but it must be numbers and have a dash (-) after it.) Then, when you are done putting the songs on, take out the microSD card correctly, and put it back in the MP3 player.
Make the circuit
The circuit is easy to make. It goes like this: Battery -> C---A---B---L---E -> Power -> Remote Trigger -> MP3 Player. The battery should NOT be a USB battery, and the power should NOT be usb power.
Connect the circuit to the brick adapter
Connect the beginning of the circuit to the brick adapter. A spot should be left out for the microSD card slot in the MP3 Player. If there is not, then you are building it incorrectly. DO NOT ADD ANY MORE BRICK ADAPTERS!
Tape the following things to the mounting board
Tape the bits, and the brick adapter, to the mounting board. Tape the battery to the middle of under the mounting board. Tape the microSD card adapter to the battery.
Switch the MP3 Player Playback Mode to ALL
Switch the playback mode on the MP3 Player to ALL. This way you can use the remote trigger to give you access to pause and play one, and to move back and forward between one, a music track.
Turn the circuit on
Turn the circuit on and off whenever you need to, and now, your jukebox is fully complete! You can always add and remove tracks from your jukebox as much as you'd like, as long as you have a computer or something that reads and allows you to access SD cards, and/or microSD cards. Happy listening!