There are some good tutorials on youtube as well, that's mostly how I have been teaching myself gimp. But I just look one up when I want to do something but don't know how. Like when I wanted to do a sunburst effect https://www.youtube.com/watch?v=BKlICU0Egcc
or when I wanted to do pushed in text https://www.youtube.com/watch?v=p1K3L7RdbKw
. But it depends how much a beginner you are. You might try Gimptricks channel https://www.youtube.com/user/GIMPtricks?feature=
I learned how to use the align button there.