Hi there @evie_7!
Don here from Shopify.
Once you delete an app from the Apps menu in your Shopify admin you will not be billed for any future billing cycles of that app.
If a new billing cycle had already started for that app before you removed it, you would still be charged for the use of that app for that period, but would not then be charged again moving forward for it.
You can learn a bit more about how this all works here on our help site.
If you feel you have been charged in error for the use of an app, you can always reach out to the developers using the contact details listed on the page for that app in our App Store to see if you would be eligible for a refund request.
Let me know if you have any questions about this or anything else Shopify-related.
Was there a particular business need you wanted to address using that app or were you just trying things out?