Levels
This can be quite tricky at first but you will soon get the hang of it. It's mainly for when you record, so that your mixes sound at the same level. Everyone hates it when they're listening to a decent mix and the sound level is going from too loud, then too quiet etc... Eventually you should learn to get it just right each time so that the levels are all the same through out.
One fairly easy way is to get a mixer with an equaliser on it, you know the flashy lights. If you do get them the same level on the mixer equaliser, the records may still sound too loud or too quiet because most records are record at different levels.
Eventually you will get it right and have the perfect mix at the perfect sound level.