Buttons and menus are named exactly as the app shows them.
Steps
Choose a master key
One key opens the vault and every lock. It never leaves this device, and there is no way to recover it.
Where: Settings › Locks and privacy
Lock a tab
Pick the tab and the kind of lock. A plain lock hides the tab until the key is typed; Encrypted also seals its rows and files before they sync.
Give it a password of its own
Tab password adds a password for that tab alone. The master key still opens it.
Choose when it locks
Locks itself sets when the tab locks again: at once, after some minutes, or never.
Open with your face or fingerprint
On a phone, keep the key behind Face ID or your fingerprint. It stays on that phone.