File and database basics
File Manager, Backup, phpMyAdmin and MySQL Databases cover most routine work. Between them you can deploy a site, take a copy before changing anything, and inspect what your application is storing.
Domains, email and SSL
Addon Domains and Subdomains map names to folders; Email Accounts and Forwarders manage mail; SSL/TLS Status issues and renews certificates. Free SSL should be on for every domain you host, without exception.
The ones worth learning properly
Cron Jobs, Error Log and Resource Usage. Cron schedules the maintenance your application needs; the error log tells you why something broke; resource usage tells you whether a slowdown is your code or your plan.
