yeah so um my upper rear break light doesnt work. i tried a bulb and nothing. the fitting is sort of loose. idk much about electronics. any ideas?

 

I would say to check the fuses, doubt it will do any good though, should be all three brake lights on one fuse.
You will want a test light or multimeter. With that see if you have power.
If you do, then the bulb has a bad connection, or it's not grounding.

If you don't have power you will have to follow the wires back until you find power. Then figure out why. Could be an plug loose, or a broken wire.
This is also where a wiring diagram is handy to see where the wires go.