If you would like to restrict access to specific content for members only, you can grant access via the settings for each Membership Plan. First of all make sure that the content is not set to Available to everyone.

Then go to Settings>Membership Plans and select the relevant membership plan that you want to grant access for.

Click on the Activity access tab and select the content page from the list.

Then click Save changes.

From then on, all members with this membership plan will be able to access this content.

Please note that you will need to repeat this process for each membership plan that you want to grant access to the content.