If you purchase a subscription your contract will renew automatically, on your annual or monthly renewal date, until you cancel,Please refer to the subscription terms in following link:
Perhaps I made the question in a wrong way.
I need to know if I have to pay every months the Creative Clod service or if is it possible to pay it only when I need to use it (for example from 15th march to 15th april, on june, on september, and so on).
Thanks for your reply.
No, if you have a subscription according to the type of the subscription you'll have to pay every month or year until you cancel.
If you think you would use the apps for three months only and then you'll not need it for another three months then our Month to Month plan would be best for you as it can be cancelled anytime it doesn't come with an annual contract for more info see the below link,