ClassPass is a monthly recurring membership, so it will automatically renew on the same day each month. On the day you sign up, you're membership begins immediately so you can get to working out right away!
You're welcome to cancel your membership or put it on hold at any time, as long as this change is requested at least one day before your cycle renews. You can change your account's plan by going to your Account Settings. All plan changes made kick in for the following cycle.