You ask questions - You answer questions - you publish trips - everything earns you credits.
The only way you can redeem them: By buying a trip package from tripoto.
1 Credit = 4 INR
Can you get a trip free if you have credits more than the value of the package?
No. Every package has a set number of credits which can be used. Some may allow 20% credit usage or some may allow 80% of the entire package price.
The only way to find out is by trying to buy a trip.