Contacts

Turn on View › Contacts, then pick the coin at the top. Contacts are stored in your encrypted wallet file.

Monero

Right-click inside the list:

Bitcoin and Litecoin

Add contact saves an address, silent payment addresses included. Double-click a contact to pay it. Right-click for Pay to, Edit…, Copy address, Copy name and Delete.

Not restored from seed

Contacts live in your wallet files only. Keep a copy of the files, or export your Monero contacts, if you want them after a restore. See Seeds and backups.