Appearing in an unoccupied space within range, a spirit that takes an animal form (you choose) with that animal's stats, though it is a Celestial, Fey, or Fiend (your choice) instead of a Beast. Your familiar acts independently, but obeys your commands.
Telepathic Connection. If within 100 ft of you, you can communicate with it telepathically. As a Bonus Action, you can see through the familiar's eyes and hear what it hears until the start of your next turn, gaining the benefits of any special senses it has.
Combat. The familiar rolls its own Initiative and acts on its own turn. A familiar can't attack, but it can take other actions as normal.
Dismiss. As a Magic action, you can temporarily dismiss the familiar to a pocket dimension. As a Magic action while it is temporarily dismissed, you can cause it to reappear in an unoccupied space within 30 ft of you.
See PHB for full details.
Material Component:
10gp worth of charcoal, incense, and herbs that must be consumed by fire in a brass brazier
Verbal Component:
Reperio Medeis Spiritus