Where is the positive and negative holes on the arduino mini breadboard?
Does anyone know what to do?

Do whatever you want to do.
There's nothing special about the +/- rails of a breadboard - they're just chunks of metal that go along instead of across, and are longer, with more holes, and someone has helpfully coloured them red/blue and added some symbols.
If you want a common place for + and - then just choose a common place for + and -.