Try the Compute Routes demo

The Routes API Compute Routes demo lets you specify an origin and destination as a latitude/longitude coordinates pair or as a place ID. To copy the latitude/longitude coordinates, find and click a location on the map, and then paste the location into the form.

If you have an encoded polyline or a GeoJSON linestring, and you'd like to view the polyline on map, go to Interactive polyline decoder utility .

After you select Get route, the demo displays the response from the computeRoutes method as a route on the map.