What do I need to get started on Garrys Mod?

I just purchased Garrys Mod recently from steam the one that updates so i think thats garrys mod 10 not sure. But I was wondering if someone point me in the right direction and tell me all the downloads i'll need to be able to make stuff, theres alot of stuff in the game already but isn't there more downloads you can get like lua m changer SWEP, garrys mod plus, or other content? and also if there is a really good tutorial site for just starting and then advanced tutorials could you please post some links thanks.