when I go to a new layer how do i know what color i use when I go back?

You can see what color you’re using on a particular layer by looking at the foreground color (located at the bottom of the Tools Palette).

If you’re on a Color (32-Bit Layer), you can then change the color you’re working with by double-clicking on the foreground color, and then selecting a new color from the Colors Palette.

If you’re on a 1-bit (black), 2-bit (black/white), or 8-bit layer (gray layer), you’re only working with the one color (black, or whatever color you chose in place of black — see Layer properties), so that won’t change when you go back and forth from that layer.

Ask away!