There are two tabs on the Product Selection page: Products and Plans.
On the Products tab you can choose which products will be available for end-users. To show all the products under certain category, click Show products. You can hide this information by clicking Hide. There is also a description for each product if you click Learn more.
On the Plans tab you can choose which Account Plans will be visible for end users in the sign up wizard. Check/uncheck boxes to select/deselect billing plans that you would like to enable for customers.
Note: Services such as Encryption and Archiving are both available for Exchange and Office 365 accounts but have independent Product Selection options. To disable the service for both accounts, it is important to uncheck both options. And wise versa - to enable the service for Office 365 account, you need to have the corresponding option checked in Office 365 Add-Ons Services group. The checkboxes do not update each other, you need to enable/disable both of them manually.
After making changes click Save Changes at the bottom of the page.