Many features are configurable for each user individually to allow administrators more granular control over a Jellyfin server. Keep in mind that Jellyfin users are entirely local and no information or metadata will ever be sent to remote servers during the login process.
To add another administrator you can simply check the box labeled
allow this user to manage the server at the top of the user options. This will give someone full access to all pages and features on the site so be careful who gets access.
You can allow transcoding for audio and video individually to prevent certain people from using too much system resources. There is also an option to enable video playback that doesn't require encoding. This is much less CPU intensive and will often fix playback issues on devices that don't support newer video formats.
Users can delete media from the library with this option, which will also remove them from the filesystem. If your server doesn't have write permission to the media files they will be removed temporarily but picked up on the next library scan. You can also enable this option for individual libraries.
If you disable a user they will be kicked off the server immediately and unable to login until the option is deselected. This is useful if you don't want to expose unused credentials on a public server but might want to keep the account around for a while. You can also hide a user from the login screen and require manual entry of both the username and password. This will prevent users from knowing what accounts have been created on the server when they login.