Here’s the excerpt from Wikipedia
The First Class AC: This is the most expensive class, with fares which can be on par with airlines. Bedding is included with the fare in IR. This air conditioned coach is present only on popular routes between metropolitan cities and can carry 18 passengers. The coaches are carpeted, have sleeping accommodation and have privacy features like personal coupes.
AC-Two tier: Air conditioned coaches with sleeping berths, ample leg room, curtains and individual reading lamps. Berths are usually arranged in two tiers in bays of six, four across the width of the coach then the gangway then two berths longways, with curtains provided to give some privicy from those walking up and down. Bedding is included with the fare. A broad gauge coach can carry 48 passengers.
First Class: Same as 1AC, without the air conditioning. Such coaches are not very common.
AC Three tier: Air conditioned coaches with sleeping berths. Berths are usually arranged as in 2AC but with three tiers across the width and two longways as before giving eight bays of eight. They are slightly less well appointed, usually no reading lights or curtained off gangways. Bedding is included with fare. It carries 64 passengers in broad gauge.
Note :- Power plug points are provided on some AC coaches, depends on your luck. One important thing about the power provided is that its 110V AC and not the standard Indian AC voltage 230V AC. For laptops and mobile chargers its okay as most of the current adapters have SMPS that can tolerate input supplies from 100 to 260V AC.
AC Chair Car: An air-conditioned seater coach with a total of five seats in a row used for day travel between cities.
Executive Class Chair Car: An air-conditioned seater coach with a total of four seats in a row used for day travel between cities.
Sleeper Class: The sleeper class is the most common coach, and usually up to ten coaches could be attached. These are regular sleeping coaches with three berths vertically stacked. In broad gauge, it carries 72 passengers per coach.
Seater class: same as AC Chair car, but without the air-conditioning.
General: The cheapest accommodation, with seats made of pressed wood. A seat may not be guaranteed and tickets are issued usually two hours before the scheduled departure of the train. These coaches are usually heavily crowded.
Now what I wanted to note was AC 3tier is more expensive than AC Chair car but Indian Railway Catering and Tourism (IRCTC) doesn’t give any benefit for AC 3 Tier travel while using Shubh Yatra Card. BTW the card is the Frequent Traveler card provided with an initial charge. The only benefit apart from getting free tickets on reaching 500 points is that you don’t have to purchase platform tickets when you have the card. Its unfair in not giving points for AC 3 tier as the charges are higher than AC chair car. I wonder who gave such great ideas to Indian Railways