[gnaffle]

There are many ways to do meditation (and many goals) but generally in silent meditation you pay attention to what your mind is doing, how you are feeling emotionally and physically, etc. To have a "reference point" you can pay attention to your breath.

http://www.audiodharma.org/series/1/talk/1762/ is a good, free introduction (this is from a Buddhist center, but the podcast applies to mindfulness in general).