Don't Install If You Aren't Prepared
Are you prepared for the macOS Catalina upgrade? If you aren't ready, you shouldn't install this upgrade yet. It only takes a little time to prepare and it is worth it.
Make sure you have a current Time Machine backup or another type of backup. While you won't likely need it, you are better off with one on hand.
Make sure you research the new macOS Catalina features and learn about what this upgrade brings to the Mac as well as what you lose when you upgrade. If you get a new Mac, you can update without worrying about the prep, since you'll either be using it as a new Mac or transferring from an old Mac.
Here's a list of things to do before you install macOS Catalina, which you should make sure you complete before you start the upgrade.