Hi there, for several days I am trying to get a background color/circle behind the logo that I have drawed in Inkscape. I have added layers, I have changed layers but it would work out, the circle always appears
on top of the logo, and not behind it. How can I manage to do this?

Thanks in advance.

Hmm... Are you sure that your circle is really on a layer below the logo?
Couple of things I'd try:

a) Go to the layers dialog and hide one layer at a time and see what happens.
b) Select your circle and press End.

Also, can you share your file so we can take a better look at it?