Where do I find it?
Configuration > Business Data > Capacity-Templates
What does it mean?
In this section you can define how many seats you can sell for a certain vehicle. You must specify how much capacity each vehicle has. For example all your green tour busses have a capacity of 89 standard seats. This is relevant so customers can not book an even that is already sold out.
What should I do?
Select how many passenger can sit in each one of your vehicles.