I use GIMP on my laptop. Its free and is similar to PS. It takes a little getting used to but it is for sure the best, free program out there.
Once you get GIMP, watch some tutorials, get to know how everything works and the basic idea on how to manipulate images.
Then I asked artists like Jellos Warmbloods, who uses GIMP also, for tips on things I was struggling on. For instances, main and tails.
Other than that its just lots of practice :),