How to outline a drawing on gimp?

Like an anime drawing? I've always wanted to post digital art that isn't crappy on deviantart, but I'm more of traditional art type of person. But anyways, I usually take pictures of my drawings and install them to my computer, then plan to make them more awesome on gimp, but it just never woks. I understand that you have to make many layers and all, and even the Bezier curve tool. The only problem is outlining the picture using the Bezier curve tool, I'm not really sure if it outlines or not. I've tried using it to outline, but it was green and thin. I tried making it thicker, and black, but it just didn't work. Please help I am soo confused. I saw and read many tutorials on using Gimp, but none of them helped me.