Jason here from Shopify Support.
Great question. Since you've already selected a plan, at the end of your trial, the system will automatically deduct the amount from the bank account that you've enlisted with us. Before the deduction, we will send an email notification letting you know the invoice amount that will be deducted. When the time comes, here's a useful guide on understanding your Shopify bill.
A reminder that before you fully close your account, don't forget to remove any recurring billing apps to avoid app charges. Also, if you have connected a third-party domain, remember to remove it from your admin; if you have a domain bought from Shopify, remember to transfer your domain out of Shopify. The domain can only be transferred out after 60 days of purchasing it according to Internet Corporation for Assigned Names and Numbers (ICANN). Since the trial period is only 14 days, you have to contact our 24/7 support after 60 days of the purchase date to transfer it out. Note that this restriction only applies to the new purchases only, not the domain renewals.
If there’s anything else I can help you out with, don’t hesitate to reply back and I’d be happy to help!
All the best,