One thing to remember is that if you eventually wanted to sell your work, you would need permission from the photographers to use their pics. Most don't mind if you give proper credit.
Check out some tutorials. http://www.deviantart.com/
has some great tutorials: http://browse.deviantart.com/resources/tutorials/
I'm not very good at photoshopping but I do it sometimes.
I made these with Gimp:
LOL. I don't remember what I used for this one. It was when I had my Taylor Lautner obsession.
LOL. Another obsession XD One of my very first edits.