You can choose actions for your website to perform automatically after a customer purchases an item ,and payment is confirmed, on the Add/Edit Item pages, in the "After Payment" section.

You can choose a member group to add the customer to after payment and the membership days - set this to 0 to not expire.  You can use this to provide access to certain page(s) of your website to the member after payment.  Also, you can choose to give Download Access to a file after payment, and choose the number of download access days - set this to 0 to not expire.  You can upload this Download Access File directly here; you can zip multiple files.  Members get a list of File Downloads they have purchased and access to on their Profile Page, Downloads section.

If you have chosen the E-Commerce Type PayPal Shopping Cart or PayPal Checkout, these actions will be performed automatically after PayPal confirm the payment has been processed, as per your instructions on the Add/Edit Item pages.  Otherwise, if you have chosen the E-Commerce Type Email Checkout option, you can manually perform these actions using the E-Commerce > List Files/Group Access Info tab.  On this page you will find the Add Access and Edit Access options.