2nd Sleeper Class, non AC. This is the regular class that Indians use. It can be noisy with vendors coming and going all night. Dust and smog will come in through the windows. These have 3-tiers just like the 3-tier A/C but without the A/C.
3-Tier Sleeper, this is an A/C carriage with three levels of bunk beds per side, so 6 beds per berth. There are 12 berth per carriage. You will get sheet service with this class. It has A/C climate so the air is filtered. This is often a security rail man at night . This is recommended for solo travelers. The price is 2-3 times that of the regular 2nd Sleeper class.
2-Tier AC, 1-Tier AC
Rajdhani express trains.
If you have a bit more ruppees to spend you can move up comfort levels. If your in a hurry and there a shortage of seats you may have to purcahse in this class. Instead of 3 bunks there just 2 or even 1 bunk per side. Rajdhani express is a worth while expense.
Shatabdi Chair Cars
These intercity express trains are good value. They offer 1-2 carriages of A/C Chair cars. The rest of the 20 or so carriages are non ac Chair cars. These Chair car can vary in comfort level, often the chairs may not recline properly. A seemly huge number of locals cell mobile phone seems to be ringing some what constantly.
Toilet facilities on Indian Trains
Generally there will be western style toilet and Indian style squat style, After a long train journey the toilet are usually filthy. the higher class train have cleaner facilities.