Singing

So, I really want to be able to sing well. I've been told a bunch of different things, from "Wow, don't open your mouth ever again" to "That was really good! You have a great voice."

So which is it?

Good or bad?

I've been singing a lot lately (even if I suck) so that I can get better and train my voice. If anyone out there knows any singing technique things that will help make me better, please share them! I've never had any formal training in singing. The radio is my teacher, if you will.