Thank you JFisher and MEB. I first select the object I want to adjust in the Background layer; then I add an adjustment layer, pick from the drop down menu, apply the adjustment to the selection and it seems to work. However, 2 other issues with selections:
1. If I try to select another area to apply a DIFFERENT adjustment to, and then add another adjustment layer, it affects BOTH layers instead of just the 2nd adjustment layer.
2. If I try to cut (Command+C) one of the selected objects and paste it into another photo, it doesn't work.
More seriously, I've noticed twice that when I use Affinity Photo for a few hours, my computer gets extremely overheated and starts making a low noise I've never heard before. What is this? As soon as I exit out of Affinity, the computer cools down and the noise stops. Please help.