The Companion System in ESO is a new feature of the game that launched with the Blackwood Chapter. This allows you to summon a Companion (basically like a 2nd character) that will follow you around. The Companion can help fight, be it as a damage dealer, healer or tank. Currently there are two Companions, Mirri Elendis a Dark Elf and Bastian Hallix an Imperial.
You can find more info about the Companion System in the Companion System Guide.
Bastian Hallix Guides:
Mirri Elendis Guides:
