I Need Help with Excel

I am trying to organize my coupons in Excell (I know-I'm nerdy). It is one of my being awake in the middle of the night projects. I somehow selected 2 sheets at the same time or something. An error has come up that says, "You cannot make changes to a list when mulitple sheets are selected." Okay. How do I unselect the other sheet so I can make changes? It locks up whenever I do anything. I click okay and try to figure out how to unselect it, and then the error pops up again. I'm stuck. It won't let me save it. It won't even let me close it. Computers are dumb.