How do I copy an image section, then paste It into a different, larger image?

It's that simple. I have used PS for many uyears, but I stopped for a bit, around 2020, then resumed in 2024. And now I find that many of my old shortcuts, such as Command-C  for "Copy ", and Command-V for "paste", don't work. I can't tell what I'm doing wrong. This is pretty basic stuff, and I can't do it anymore. Should I switch to Affinity? Any and all help will be appreciated. I'm on an M1 Mac Mini runing Sequoia 15.0.1.