What are reserved seats and non-reserved seats?

Reserved seat: Specific trains and seats will be automatically assigned. You can't select preferred seats for the time being. If there isn't enough capacity on the train, your group might not be able to sit next to each other.

Non-reserved seat: You will have better flexibility in taking any train on the specified date/route. However, seats are not guaranteed and are available on a first-come, first-served basis. You might need to stand throughout the journey if the train is full.