Welcome to the forum. First I would try to close the app by double pressing the home button which gets all your open apps on the screen and then you just swipe them away 1 at a time. After you swipe the App Store app away I would power the ipad off and then back on and try it again. If it still doesn’t work then you can do a soft reboot by pressing and holding both the power button and the home button and don’t let them go until after the ipad shuts off and the Apple appears in the middle of the screen.