Basic questions on charging for subscription

[yanasemour]

Hello!
Could you please provide me with all the possible information on how charges in Apps happens? Because we have an app and we have people with subscriptions and no one has been charged for 10 days(trial period is 3 days).
I understand that if the person is on Shopify trial he'll be charged as soon as shopify trial ends.
Also, I guess that if the person subscribed to the trial but didn't sign in the store since then, he'll be charged as soon as he log in.
What other things we need to know? How can we check what type of Shopify user has(trial or not)? Where to read about it?