The number of times you are able to visit any studio in the ClassPass network depends on your plan type. You can find information about how many times you are eligible to visit a studio under 'Your current plan' in your Account Settings. If a studio or gym has more than one location, you can visit the number of times allowed by your plan across all locations, not per location.
If your ClassPass membership begins on October 15, you would have between October 15 and November 14 to visit a studio the amount of times allotted by your plan. Then, on November 15, your month would renew and your number of visits would refresh.