While you have a familiar, you have one of the following benefits based on your familiar's Speed. If a familiar has more than one special Speed, you choose the benefit in such cases.
Burrow Speed
Difficult Terrain doesn't cost you extra movement.
Climb Speed
You have a Climb Speed equal to your Speed.
Fly Speed
As a Bonus Action, you can gain a Fly Speed equal to half your Speed until the end of the current turn.
Swim Speed
You can breathe underwater and have a Swim Speed equal to your Speed.
No Special Speed
Opportunity Attacks against you have Disadvantage.