How do I copy and paste my painting?

[denzjos]

I think you want the drawing on a transparent layer. First look if the drawing has an 'Alpha Channel' (right-click on the layers dock and see if 'Add Alpha Channel' is activated. If not, add it. Then on the drawing remove the white with 'Colours / Colours to Alpha' (on the gimp main menu). White is the default colour on this, so click on 'ok'. The white colour disappear. Now you can make a new layer with any colour you want and put it under the drawing layer.