What is the difference between classes and caste ?

Castes are usually more religious in context (such as in Hinduism) and are less socially flexible; once you are born into a CASTE, it is almost impossible to move up the caste system. Classes enable more flexibility; you can more easily move from a lower class to a higher class compared to castes, which you are born into and can never change.

Primary sources are usually  more accurate and are written by someone who experienced it or witnessed it. secondary sources are those who heard of it after the fact that can lose details and or twist the event in a light that benefits them.