This page is taken from the in-game tutorial which you can access by pressing F1 from within the game.
To add someone to your list of contacts, press the O key to open your Contacts Menu. Press the E key to open the "Add Friend" menu to begin adding a friend. Type the name of the player's character or their UseriD preceded by an @ symbol.
Optionally, you can add a custom message to your invitation, to let them know who you are. To send the invitation, click "Request".
Friend requests can be sent even if the targeted player is offline. The request will remain on their Notifications Menu until the request is accepted or declined.
♦ To access the Notifications Menu press the N key Once another player accepts your invitation, each of your UserIDs will appear in the other player's list of contacts.
♦ To access the Contacts Menu press the O key It is important to understand that your friendship is at the player level, not the character level. This means that you will be able to see and contact your friend no matter what character either of you is currently playing.
To ignore a player, open your Contact Menu by pressing the O key. Click the "Ignore" icon in the upper right corner of the menu and press the E key to add a player to your list of ignored players, either by entering one of their character names, or by entering their UserID, preceded by an @ symbol.
Players that are violating The Elder Scrolls Online Code of Conduct should be reported to Customer Service. Type "/help" in the chat line to bring up the Help System Menu, then click on the "Ask For Help" icon on the upper right, choose "Harassment" from the list of categories, and file a report.