During wallet setup, you are shown a recovery phrase. Write it down exactly, in order, on paper. This is your primary backup.
Consider stamping the phrase into metal for fire and water resistance. Store the backup in a safe, dry place.
For larger holdings, store a second copy in a different physical location so a single disaster cannot destroy your only backup.
The only way to be sure your backup works is to test it. A small test restore, or a careful verification, confirms you recorded the phrase correctly.
Do not store the phrase in the cloud, in a notes app, in photos, or anywhere digital. Do not share it with anyone.
A wallet without a proper backup is a wallet you could lose at any moment. Back up first, fund second.