Instagram v10.7.0 is the latest version of the Android app, and the company appears to be testing a new feature that would allow users to post multiple photos in a single post. Something that is not currently available on Instagram. The feature works about as you would expect it too, but it is not fully-functioning just yet. It's likely only going to be available for a handful of users while Instagram tests out the feature.
To put it simply, Instagram will allow users to upload up to 10 photos in a post and upload it to their timeline. Your followers will see the album in their timeline and be able to scroll through them and like whichever ones they want. Posters will be able to edit each photo individually, adding whatever filters they want to each photo, or to just a few of them. Instagram has not yet announced this feature - which is because it is still in testing - so don't expect it to be working when you do get the update to this new version of Instagram. The interface appears to work the same as it does currently, you are just able to swipe through your photos, instead of having just one in the "edit" screen.
Companies like Instagram typically will test features in a new version of their app with a small amount of users. This is to get feedback from their users before they send out the update to everyone, or make the feature available to everyone. It's especially important on a popular app like Instagram, that is used by millions of people. As company's don't want to announce a new feature that just simply doesn't work, or may crash the app. Of course, Instagram does plenty of internal testing, but that doesn't mean they'll find every single bug that may pop up in the app. It's unclear how long this feature will be in testing, but once Instagram announces the feature, it should be available for everyone, likely in a server-side update. Something that many app developers have been doing with new updates in the last few years. Making it easier to send everyone a new update without forcing everyone to download an updated APK.