Hinduism is a polytheistic religion, which means they believe in many gods. Hindus also believe in reincarnation, which is the rebirth of one's spirit. Karma and dharma is what Hindus think influences their next life. Practicing good deeds will put them in a higher social class in their next life.
The caste system is the rigid social structure in India. There is little to no social mobility until reincarnation occurs. Birth and karma determines someone's caste. Priests are at the top, soldiers are under them, then merchants and traders, followed by the laborers, and ending with the untouchables. The untouchables are so low in the caste system they can't interact with other social classes.
Gandhi wanted to get rid of the British rule and wanted India to have self-rule, an Indian man ruling. This made him a nationalist. He used civil disobedience instead of violent tactics, an example of this is the Salt March. The Salt March is when Gandhi led a peaceful march to the sea to get salt. This disobeyed British law that the Indians had to buy it from the British.