Do you need reservation to visit Zion?

Not yet! But you'll want to arrive early.

No, you don't

Reservations are not necessary, arriving early is recommended. Advice to park the car outside Zion and take the (free) shuttle bus to the park.

And you will have to find a place for your car. It's very crowdy

No, but if the parking lot is full, you'll have to park outside the park and shuttle in. You have to pay for street parking too now.