These three settings decide what happens in the gap between you opening the vault and somebody else picking up your phone. The defaults are deliberately cautious, which occasionally means the app asks you to unlock more often than you would like. That is adjustable.
Face ID, Touch ID and Optic ID
Optional on supported devices, and off until you switch it on. With it on you unlock the way you unlock everything else. With it off you type the master password each time, which is slower and is the right answer for some people. Neither choice changes how the vault is encrypted: biometrics unlock the vault, they are not the key to it.
Auto-lock
The vault locks itself after a period of inactivity rather than staying open until you close the app. Shorten it if you are often somewhere with other people; lengthen it if you are filling a lot of logins in one sitting and the re-unlocking is getting in the way.
The clipboard timer
When you copy a password, it clears itself from the clipboard in under a minute. This matters more than it sounds: the clipboard is shared across apps, and on Apple devices it can travel to your other machines through Universal Clipboard. A password sitting in it indefinitely is a password any app you open can read.
Appearance
A wide choice of light and dark themes, or follow the system setting. Cosmetic rather than security, but a vault you open several times a day is worth having look like it belongs on your phone.