In order to restrict content to registered members, it is necessary to create the access level(s). To create the first level, go to Memberships | Settings, click on “Levels” link and then click on the button “Create a Membership Level:
Fill in the requested information about the level. In the final section, you can indicate the post categories that only members of this level will be able to access (to restrict access to pages, see the corresponding section in this documentation).
Don’t forget to click on the “Save Level” button to confirm.
Repeat this procedure for all levels you want or need to create. More detailed information can be found at https://www.paidmembershipspro.com/documentation/initial-plugin-setup/step-1-add-new-membership-level/