About How I can Get good at drawing on Computer Paints Like "GIMP" ect..?

Ok, see I've been doing art at school for like 3 months and I've been pretty good at it. And I get A's. But see I'm a big Fan of Dragons. And a Fan Of *Deviant Art* nearly most of my time on that site because The artiest are so good! and I want to draw like them!. I've been drawing dragons for a while and i love them....But I only draw on paper.. Witch I'm quiet pissed about. See Deviant Art is Computer Painting Art. And I cant draw on the computer because its hard to control the mouse I can only do it on paper...And I'm asking you. How Do I get good and Better at drawing on Computer Paints like Gimp? and Draw my stuff to let people see I'm very good at it? ..Please reply.