I learned most of it from a forum named Anizone. It made me work harder, I was also part of a graphics forum back then too that kind of helped. But not as much as Anizone did.
like most people said here, youtube and google help a ton. I started from messing with the classic photoshop 7 and doing a ton of trial and error with it.
I started learning on forums by making sigs, because everyone on the first forum I joined had awesome ones and I wanted to make those. I quickly realized sig design wasn't for me and moved on to other things, but still continued to learn on forums, through tutorials, etc. I've also now taken a few classes on it but most of them were just covering what I had already taught myself.
I did not learn from anywhere or school. I look at a layout then think about the theme and try to be original to that particular site.
I gaff of my idea from free public domain gfx on the web in search then I load up Corel-X/Adobe and then I edit/resize/filter/whatever. I upload it to my image hoster account for the admin to look at/review.
If he/she gives me the go I will do the whole site/board or whatever.
I have/get temp admin rights when I do this that's why I do not do it for any profit on boards, and if the owner is a paranoid person I will do all my work online in front of him so he can see I wont enter other areas in the ACP.
When I am done I have the owner drop me back down to a regular user.
I never messed with any board functions other than what I am told.
I actually just finished about 2 hours on buttons for a board..Buttons! Go figure?
I only do this for friends a this point. But I do whatever my buds want/ask.