Start with the community created FAQ. Follow all of the steps in the FAQ exactly in the order given. 
This is a very popular integration and a lot of people are using it. But you can’t use just a virtual switch. You have to use a virtual device which is both a switch and a sensor, so that turning on the switch makes the sensor look like it is open and turning off the switch makes the sensor look like it is closed. The FAQ will walk you through the steps.