Fausto, Welcome to the RT
Sometimes it is hard for long times users of Photoshop to explain to a novice user because they usually don't understand the tools or the terms. It can be like a brain surgeon trying to explain how to remove a tumor to me. Photoshop is just so deep and broad that finding a starting point can even be a problem.
For example, to erase a background, you have to know how to make a selection. There are dozens of ways to make selections, so the method you use and the tool(s) you use would vary depending on the complexity of the graphic.
I'm a visual learner and when I started out, I bought a couple tutorials on CDR that had sample files to work along with. I highly recommend the
Lynda series. If you can't afford to purchase a
PS CS series, they also offer a deal that for $25 a month you can log on and access the videos all day every day 24/7. That's a whole month to explore and learn the basic tools and terms.
When I get a new program, or a major update to an old one, I do the $25 Lynda deal and nights and weekends really get a good overview of the application. A tip here... if you do th $25 deal, as soon as you sign up, go back and CANCEL. Your credit card will have been charged for the month and you won't get caught being charged another month if you forget to cancel.
I'm not trying to discourage you, but you have a lot of work (and fun) ahead of you just to grasp the basics. Look around in the tutorials, google photoshop tutorials and buy a Photoshop for dummies book to help you learn the terms so that when you ask us how to do something you will have some idea of what we are explaining. :-)