How to call these two functions SignBytes() and SignProposal()

[beatlec]

How to call these two functions SignBytes() and SignProposal(), and how to pass in parameters? Where do the parameters come from?

For example, I know the private key of my wallet, how to convert this parameter? what is the parameter b in function SignBytes ？

Calling SignProposal() I got the signature result (clientDealProposal.ClientSignature.Data ) as "signature data", not the actual signature value. This makes me feel very strange, I don't know how to convert the private key?