The decoderawtransaction RPC turns a serialized transaction in hex format into a JSON description of the transaction's details.

How is this used?

You've been handed a secret message written in a code that looks like a random string of letters and numbers, this code contains important information, but it's indecipherable without the right tool to translate it. The 'decoderawtransaction' command acts as that translator for Bitcoin transactions. It takes a transaction encoded in a complex format (hexadecimal) and converts it into a format (JSON) that's easy to read and understand, laying out all the details of the transaction such as who is sending what, to whom, and with how much fee.