maargamitra.in AIR means All India Rank — your rank from the entrance exam, out of everyone who took it. On this site we just call it Your Rank.
Every programme also has its own number, called the Cutoff Rank — roughly, the rank of the last student who got a seat there. The rank finder just compares the two.
Lower is better
A lower rank is a stronger result — rank 500 beats rank 50,000. If your rank is better (lower) than a programme’s cutoff rank, you’d very likely have gotten a seat.
What this site doesn’t handle yet
Right now you can only enter one plain rank number. Category-based ranks, gender-specific pools, and home-state quotas aren’t supported yet, even though real admissions do use them.