Beginning with Paths

Bezier selection is a powerful tool in The Gimp. The rectangle- and ellipse-selections are not very flexible if you happen to need something more special. And since many of us gimpers don't have a graphics tablet, it's not so easy to make the mouse pointer move the way you want. Bezier selection fixes the problem by using smooth mathematical curves instead your own shaky mouse trail.

Tutorial at GIMP.org

Also read the second part after you finished the first.