I need some help, maybe a tutorial, or a step-by-step, to make this figures of Harry, Ron and Hermione for a fondant cake for my daughter's 10 year birthday... please!! Is for thursday!!! Thanks a lot!

Here is a pretty good tutorial for a general boy fondant figure. You could use this to help and just change up the details to make them resemble the Harry Potter characters. Hope that helps a little 

http://bakehappy.blogspot.com/2012/10/fondant-figures-tutorial-little-boy.html#.UWsKbCtxte4

Thank you very much Shannon!!! It's just what i was looking for! It was so helpfull!!! I´m so happy now!!! Thanks again!

You are very welcome! Hope it all works out. Post a pic after they are finished...I would love to see!