R Stone

Hi, I have a cut out with a transparent background which I would like to drop onto a plain coloured background. Fairly simple if I knew how to create a plain coloured background and best way to drop this onto it but I have no idea how to do this and can't find any video or question that will tell me. So if anyone can help me please that would be great. I only usually use this or photoshop for basic corrections so don't ever use layers or anything even remotely advanced.