Hi @debasish,
The reward field specifies how many rewards, in MicroAlgos, have been distributed to each Algo since genesis. See https://github.com/algorand/go-algorand-sdk/blob/32dccacfceedfa473edfc9a69101237f1cecb69f/client/algod/models/models.go#L445
The fields frac and rate are explained in https://github.com/algorand/go-algorand-sdk/blob/32dccacfceedfa473edfc9a69101237f1cecb69f/client/algod/models/models.go#L448.
To understand better reward distribution, see https://www.algorand.com/resources/blog/rewards-technical-overview.
The proposer field is the address of the account that proposed the block. See https://developer.algorand.org/docs/algorand_consensus/#block-proposal