The insert process creates a Contact and returns a header message containing their unique id and a url in the Location field (picture below code). To add further information (contact details, tags etc) you need to update the person using this id.
Use net.http.get for reading contact details:
Use net.http.post to create new contacts:
I took a snap of an Iguana annotation showing the returned Header message (return H in code above). The Id of the new Contact is highlighted
One of lovely things about RESTful APIs like highrise is how beautiful they are to debug, you just use an ordinary web browser to look at the data going over the wire.