Article: The "Acquaintances" feature essentially drops the priority level of its occupants' posts to the lowest possible level, meaning you'll likely never see posts from friends in the Acquaintances group. If you aren't logged in, you'll need to do so with your Facebook email and password first. This is on the left side of your Facebook page; clicking it will take you to your friend groups. This should be toward the top of the page. This is in the top right corner of your Acquaintances page; you can type friends' names to add them here. You can add as many people as you like to this list. You may need to refresh your Facebook page to get rid of Acquaintance posts. When posting a status, you can click the "Friends" option next to the "Post" button and select "Friends except acquaintances" to exclude your low-priority friends from viewing your status. You may have to click "More Options" at the bottom of the menu to view this option.

What is a summary?
Open your Facebook page. Click your "Friends" tab. Click "Acquaintances". Click the "Add friends to this list" field. Click a friend's name to add them to "Acquaintances". Return to the News Feed when you're done.