Recently, I was talking to someone about using GPG. The question came up: How do I use this?
I humbly offer the GPG Mini Howto. It's got everything from Installation to Key Management and a section on front ends and email clients.
As good as that is, I'd also recommend Gmail users check out the firegpg plugin. It helps a lot with the GPG / Gmail combination by adding some useful buttons to the Gmail interface. Doesn't get much easier than that.