layers help

I'm a new member and I would like to ask your help. I created a new layer and then a gradient fill but I can't paste the whole new background to the current background that I would like to change bec. there's sorta lock icon next to the layer. how do I change the background? pls. teach me. also, how would you ctry to delete an element of an image and not have a checkerboard appear on that image? Also, how do I attach a picture here?

1. Position the layer you want to have as the background right on top of it and press CTRL-E to Merge layers down.
2. The checkerboard appears because it means that area is transparent, without color, vacuum, whatever you want to call it. If you want to have like a color under it while working on the pic, just put a layer beneath it and fill it with whatever color you need.
3. File attaching isn't allowed. You're going to need to link to the image to the remote host.