Hi Liz,
Pinching is overused as a technique. It rarely makes a
plant bushier, because new gowth usually pops up in the same place that you pinched. It will keep a
plant from getting larger, if it is done constantly. The
plant doesn't care if you use your fingernails, finger tips, or pointed scissors.
Pruning is done with a sharp tool and it involves cutting off more than just a newly emerging bud. This is the best way to keep a
plant compact and bushy.
Trimming usually refers to the removal of dead or dying growth. A sharp instrument usually works better, but some trimming can be done with your fingers if the dead leaf comes off easily.
All clear now?