The right side of the Peloton tablet screen is known as the leaderboard. The names that appear are either people who are currently on the ride live with you now, or people who have previously taken the workout (depending on if you have changed the filters).
The first number, to the left of the profile picture, is your rank on the leaderboard. If you are doing a live ride your rank will be out of the total number doing the live ride. If you do a workout on demand later, your rank will be out of people who happen to also be doing the ride currently. You are able to change your filters to instead see your rank out of everyone who has ever taken in.
The profile picture of any users can be clicked on to send someone a high five.
Next, you will see people's leaderboard names, as well as the location, bio, and tribes the users are part of.
The last number, on the far right, is your current total output. This is a combination of your resistance and cadence. This number can be used to compare how difficult this ride was compared to other rides, as well as to "race" against other members.
You will also see a line on the leaderboard that says "X minute personal record (YYY) ZZZ". The YYY is the total output for the ride or workout where you had the highest total output ever, known as your PR or Personal Record. The ZZZ number is your average output required to match the same output as your PR. If your current entry on the leaderboard is above this line, you are on pace to get a new PR. If your current entry is below this line, you are behind your previous PR pace.