You can do a lot with that (also pixlr.com) but photoshop, you can do everything with that And it works fine
Paint.net has all of the tools of photoshop and it's free, and Gimp has all of the special effects of photoshop.
Legally? Maybe if you go to an art school or something where they have an agreement with Adobe, but I don't think that's the case for most people.
I will do that as my study, but for now I have it from a download link (not legally but when I go to school, I will get the "real" one) And yeah, you have to try it, if you want to know if you are good in it, I dont want to pay a lot of money if I'm not sure if i am good at it and! you have to buy it if you want it for your work, if you dont do that, you cant find a job! For now, I'm still learning (at my own)
If you don't want to spend a lot of money, then get either of those two free programs (the gimp and paint.net), or get paint shop pro. It has almost all of the features of photoshop and the current version (X) is like $99.
I still use paint shop pro 8. I tried the demo for PSP X but I don't remember what was supposed to be new, besides the look.