Backup Your Mac
Most users will not need a backup during the macOS Mojave installation process, but everyone should have one.
There is only a small chance that something will go wrong and that you will end up needing to restore to your backup, but if you need to and you don't have one you will be very upset.
This is the best way to make sure your photos, documents, apps and other data are all safe. You may already be backing up your photos and other documents in iCloud or another service, but it's still a very good idea to have a full Mac backup.
If you already have this setup, you should go to Settings -> Time Machine and make sure you have a recent backup. This is especially important if you use a laptop that you don't always plug in to a hard drive. Here's more on how to use a Time Machine to backup your Mac.
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