How do you use UV editing for coloring a model?

I’ve been trying to work on a low-poly character tutorial, and I’m trying to change the model’s color. However, when I place the bit to change the model’s color on a different square, nothing happens. What do I do? I don’t know how to change the color to a different one and reduce the color-changing shape to just one pixel. What do I do?

Right now you are in edit mode. You need to be in rendered mode or do a render to see the changes.