Hi Hocer, I can see you're only new here, but please practice using the Forum search facility before jumping in and asking questions that require a book long answer.
Welcome aboard and good luck.
You could start by wandering through the Trainz Resources Directory. By using the search facility there you will find all about GIMP, where you can get it, where to go for tutorials and where to start.
Please look at all the other tutorials. They're all there to help you and save people on these forums from having to repeat what has been written 100 times before.
