The Go Tool is a tool in Isle of Tune used to release the cars and let them go around the road. Oddly, it looks exactly the same in the website as it is in the iOS version. Once you've inserted some road and cars into your island, then click on the Go button to let them go! While viewing shared islands, you will notice that it automatically selects the Go button, meaning it will go immediately after you visit an island. Once you click the Go button, it will be replaced by a red Stop Button.
Warning! If you don't insert a car while clicking the Go button, then it will tell you to put one in, showing the icon like the one below: