Custom_Operation`s questions

[dark.sun]

Hello, everybody!.
We have task for integration with Bitshares. We need to use Custom_operation for store custom data.

For example, if we need put data about car ID or something else, how we can do it with custop_op?

We can begin build transactions, put any data to data field, but how we can use it? Just parse it, or something more? How we can use "extensions" and "required_auths"?,