"There is no special setup for hands-free calling with Google Home. It simply uses your personal contacts or nearby businesses based on your location to place calls.
All you have to do to start a call is say, "OK, Google, call [contact name]." You can also say things like:
"OK, Google, call the nearest coffee shop."
"OK, Google, call Rocky River Coffee."
"OK, Google, call the post office."
"OK, Google, call dad."
"OK, Google, call Jason Cipriani."
How to make calls with Google Home - CNET