Need help with importing a picture with Paint.net, please.

I'm trying to bring several pictures onto a page. I've done it before, but I'm missing a step now. The original picture I open stays there and the new one is on top of it. The steps I have written down are. File/open, use rect. tool and trace, click copy, edit/paste into new layer. It seems like I am missing a select step, but I don't find anything that just says "select". I can't find the tutorial I used before. TIA