Look for tutorials on the programs that you want to learn how to use.... Photoshop is the most common.

I'd also start a personal project so you have an objective to work towards. Maybe a personal website or an art exhibit...

You can learn photoo editing by see thisis video.. its really helps you..do you see this video?it makes me an editor :p its really helpful. now i can do advance type of editing. http://t.co/GZ0guAv50B