what is this icon it won't go away I have an icon on the top bar of my phone that looks like a square with 2 hills. It won't go away when I clear it.

It looks like the first icon on the top in this image:
As stated in the comments, this is the screenshot icon.

If you pull down the notification bar, you should see a notification that says "Screenshot is being saved" (it's not "Screenshot was saved" because you can't swipe it away and it's not "Couldn't have screenshot" because it doesn't have an ! in it).

It's possible you accidentally hit the key combination to take a screenshot (like Power + Volume Down) and that made the notification.