There are some advanced functions that only provide to users joined membership, because as you know, making software is hard, and we want to make x3 note a great app, we need your support, and as a supporter, you will get more advanced functions.
Duration of membership
Subscription membership will automatically renew, there are two types of time range of subscription: monthly and yearly, once you purchase the membership, you will get access to the advanced functions immediately.
The subscription fee will be charged automatically for each subscription cycle, once you cancel subscription, your membership will be unavailable from the start of next subscription period.
For the first time subscription, you will get one week extra free time for monthly subscription, and one month extra free time for yearly subscription.
You can cancel membership at anytime, if you don’t know how to do that, here is a guide from apple.