You summon a familiar, a spirit that takes an animal form you choose (ex: bat, cat, hawk, lizard, octopus, owl, snake, fish, rat, raven, spider, or weasel). Appearing in an unoccupied space within range, it has the stats of the chosen form, though it is a celestial, fey, or fiend (your choice) instead of a beast.
Your familiar obeys your commands. In combat, it rolls its own initiative and acts on its own turn. A familiar can't attack, but it can take other actions. When the familiar drops to 0 HP, it disappears. While your familiar is within 100', you can communicate telepathically. As an action, you can see through your familiar's eyes and hear what it hears, gaining the benefits of any special senses the familiar has. During this time, you are deaf/blind with regard to your own senses. As an action, you can temporarily dismiss the familiar. It disappears into a pocket dimension where it awaits summoning. You can also dismiss it forever. As an action while it is temporarily dismissed, you can cause it to reappear within 30' of you. See PHB for more.
10gp worth of charcoal, incense, and herbs that must be consumed by fire in a brass brazier
Reperio Medeis Spiritus