Calendar App disappeared

Suddenly my calendar app is gone from my iPad. I have looked several times for it. I have even opened the blocks I have organized related apps together several times. I have looked for it several times in the App Library. Simply not there. I go to download it in the App Store and when I do the app download page says “Open”. I click that and it opens fine with my appointments all there. Calendar is also listed in the Settings app. It also shows as a widget on the page previous to my Home Screen. Still I would like to get it back on my homepage. I noticed a few days ago my homepage icons were rearranged but didn’t notice why. I’ve no idea what’s going on. I still miss DOS, when you knew what was on it, what it did, and how it got there.