Other cultures of the ancient Near East (Mesopotamia in specific) taught the concept of divine ledgers, thought to contain decrees from the deities with regard to one's rewards and punishments in the afterlife. This reference is Exodus is meant to be understood the same way.

Basically God is pronouncing judgment on the people who rebelled against Him. Moses is offering to take the judgment upon himself, an offer that God rejects; the people who sinned will bear the punishment for their sin.

verses 32-35: im a bit confused about the exchange here. mostly about what they mean about the blotting out of the book and such.