Make sure you have an external storage device connected. Something like a USB hard drive or massive USB flash drive.
Open SYSTEM PREFERENCES (the gray gear looking icon or whatever it is) and choose Time Machine.
Choose SELECT BACKUP DISK
This first backup will take much longer than later backups. Time Machine will keep adding backups to the external storage until it is full, then it will automatically delete older backups and add new ones.
You can do manual backups or allow it to do hourly, daily, etc. backups. Time Machine puts a menu that looks like a clock in the upper right corner of the screen.
For MacOS Ventura click the Apple Menu in the upper left of the screen and choose SYSTEM SETTINGS.
- Apple Menu -> System Settings -> General -> Time Machine
Now choose "Add Backup Disk" then choose "Modify Settings"
Disable Encrypt Backup to save yourself time and grief. It is automatically enabled in Ventura.
The Options Button opens and interface to allow you to customize Time Machine settings.