Step: Object Construction. Concatenate fields.

To compute value of result object wrap it with parenthesis {car: (.make + .model)}.

If you need constant strings, use double quotes " like {car: (.make + " wroom!")}.

{
  "firstName": "Charles",
  "lastName": "Doe",
  "location": {
    "city": "San Francisco",
    "postal-code": "94103"
  }
}

{
  "name": "Charles Doe"
}