Now, I don't have your history textbook with me, but I'll try to answer them as comprehensively as possible from my knowledge.
1) The custom of burying the dead with their material goods was a belief of the early civilizations, termed as the concept of 'life after death'.
2) The answer would evidently be early humans taming animals. The value of domestic animals in today's world is unparalled, especially for agrarian areas of the country.
3) Lord Indra was the deity of the rain. Rain is vital to the economic prosperity of any civilization as it controls agricultural output. Therefore to please Lord Indra, the hymns were in praise of him. Varuna was the lord of the oceans. The oceans were important as they were the key to sailing and trade in early times.
4) It is similar to a council of members that take a common decision as a group.
5) Pottery was one of the more popular means of livelihood for people of Harappa and Mohenjodaro.
6) Rulers of ancient times recorded their victories on hard rocks or pillars so as to ensure durability of their message and to make sure that it does not get lost with time. Papers were not invented back in the period of Harappa civilization.