If you cancel your pro subscription, your plan won`t renew the following month or year (depending on your plan type). You`ll still have Pro access until the end of the period you paid for.
Keep in mind that if you have a discounted subscription rate, you`ll lose that price if you cancel your subscription.
This applies to subscriptions purchased on the website and in the mobile app (App Store / Google Play) alike. App subscriptions are cancelled via your Apple ID or Google Play subscription settings.