How do I create buttons in the infowind on the marker with Google Maps api V3?

I am creating a web application on Google map api.I'm thinking of developing an app that allows me to search within a certain range in the place library and create my own directions by searching for routes with hits.

So I'd like to add a button to the infowind displayed on the marker and register it as a transit point, but I can't find a way to add a button to the infowind.

Please let me know the basic one.