Gauge Help!

I am a self taught knitter and am addicted! I need help with some basics that I cannot for the life of me figure out so here goes –
I need to know what make up a stitch and how to count them on the gauge chart – this sounds stupid, I know, but I am making a sweater and want to get the right size. Books show gauge but never what constitutes a stitch – How do I do this?

This will help

Found a video