I sympathise with the questioner. I'm no pro, but I've some experience using Photoshop, Aperture and Pixelmator; I have struggled to do anything with Affinity Photo other than crop images. It seems that hours of watching training videos is necessary.
I suggest to the questioner to make sure that the Layers panel is open, and make sure that the pixel layer is selected before trying anything. Otherwise, nothing will happen. But this is not a recommended way of working. The next thing is to figure out how to use adjustment layers (definitely not there yet).
