With GMaps.js you can draw a route between two points this way:
map.drawRoute({
origin: [-12.044012922866312, -77.02470665341184],
destination: [-12.090814532191756, -77.02271108990476],
travelMode: 'driving',
strokeColor: '#131540',
strokeOpacity: 0.6,
strokeWeight: 6
});
You must define two points (origin and destination) and color, opacity and weight of the route in the map.
Also, you can define a travelMode: driving, bicycling or walking. Default is walking