Here you can assign the currently edited role to be included as part of special types of website membership. All permissions allowed by the role will be granted to users who purchase (or otherwise obtain) the specified memberships.
To add the role under a membership, click the Add membership button and check the boxes next to the appropriate memberships in the displayed selection dialog. Only memberships that belong under the same site as the given role can be chosen (global roles may only be assigned under global memberships). The role can be removed from a membership at any time using the checkboxes in the list together with the Remove selected button.
Additional information can be found in the Developer's Guide -> Development -> Membership, permissions and security -> Memberships chapter.