Facebook is testing a new tab for pages called Groups, and you'll find this new tab on the left-hand side of certain pages on the Facebook website alongside other links like Photos, Videos, Events, Likes, and more. The Groups tab isn't appearing on all pages on Facebook and it isn't showing up on personal accounts. Rather it's meant for brands such as HBO to have a new way to reach individuals. From the user side of things, this new Groups tab is focused on providing users with a portal to finding Facebook groups about a brand that are official group pages, so if you're someone who is looking for an brand's official Facebook Groups, this is how Facebook is making it possible to get to them more easily.
Facebook hasn't detailed how many brands it's currently working with for testing this new Groups tab, but HBO is one of the first ones. That being said, HBO also only has one Facebook Group listed once you click on the link - the official page for Big Little Lies, though with how many popular series shows they have on their network it wouldn't be a surprise to see more popping up soon, and with Game Of Thrones' new season on the way an official Group page for the series could very well find a spot in this new tab.
According to Facebook there are around 2% of brand pages that experimenting with the new tab and those pages have already created official group pages and are now linking to them from their brand page. While 2% of brands might be a small number at this point, more brands are expected to be using the Groups tab on their pages to link to official groups later on this year with an expected time frame of sometime in June. This means that in just a couple of short months more users are going to start seeing official Groups being linked to from the brand pages of their favorite brands. For users who follow the brands they love on Facebook, keep an eye out for the tab to appear on the left side of the page. In addition to making it easier to connect users to official groups, it also opens up more control for administrators of a brand page to post on an official group page as the brand.