The Ladder is displaying the top earners of all users using Timebucks on a given day. If you are one of the Top Earners of that day then you will automatically appear on the ladder and be eligible for bonuses.
This is a monthly competition where the person with the most referral commission from referrals that have signed up this month win a bonus. This is NOT a competition for who has referred the most people, it is who has the highest Referral Commission, so your referrals have to actually do tasks. But remember, it only includes referrals that have signed up this month AND who have verified their ID, it does not include referrals that have signed up before that.
This is a List of what other users are doing in your region or in your country so you can get ideas of how to earn more.