For those who are thinking of giving this fine game a go, here's a nice guide to get you started:
http://www.purgegamers.com/welcome-to-dota-you-suck#.UuLhWRBFBaQ
I warn you now, this is a tough game with a brutal learning curve so don't expect it to be an easy ride for your first couple of games. Get past that initial hump though, and a whole world of fun awaits....