Very hard to say. I can't imagine how it'd be to start now. Even as I started in mid 1990's, I still learn new stuff every day (almost). The amount of information available today, and the features photoshop has are a huge huge ordeal to learn from scratch (I'd imagine). It's almost like second nature to me already, so I really can't say where I'd personally start today, with 0 knowledge.
Depends a bit on what you want to learn. Pick up a few books about color psychology, not just for the advertising potential etc, but they usually have a lot of information on how colors match, explain the differences between rgb and cymk colors, luminosity etc etc. You kind of need to know a thing or 2 about colors if you want to design, you can know all the features of photoshop and still make designs that make ones eyes bleed if you're basically colorblind ;)
The second step would be to just play around with photoshop, do some tutorials etc. I doubt I'd ever enroll to photoshop classes if they weren't a part of my education. The bad thing about learning something like photoshop is that you won't learn it over night, you won't learn it in a week, not in a month... so, if I didn't know photoshop now, I doubt I'd have time to learn it. If you are already in college, and you have the opportunity to take classes on colors or/and photoshop, take them.
I don't think there's a better way to do things than just play around with it, you just have to make sure when following tutorials that you understand what and why something is done, if you just follow the instructions you don't know how to implement the stuff you just 'learned' to anything else.
hehe.. that was a long and pointless post
You're welcome