The feature is available in one-on-one conversations as well as group chats with as many as 20 people; everyone will need to use the 8.26.76 preview build on iOS, Android or desktop for it to work. If sending read receipts is not your jam, you can turn them off in your privacy settings and they are disabled in any case if your status is set to invisible. That said, to see read receipts from others, you'll need to have the option turned on. Assuming the test goes well, the feature should roll out to everyone at a later date.
Of course, a litany of other apps have had read receipts for years, including iMessage, Whatsapp, Twitter's direct messages and dating services. Facebook even has them for events, so you can see which of your friends are ghosting your birthday get-together invitation. So, it's about time Skype joined the club, even if it means you might need to be a little quicker with your replies to avoid hurting your buddies' feelings.