If you're doing any kind of paid advertising, you've got a built-in Conversion Tracking Tool.
From the sidebar, select Site. Then click on Tracking.
How does it work?
When you do Facebook or Google advertising, you will get a tracking pixel. What is a tracking pixel? It's basically two lines of code.
If you copy and paste that code, when someone has come through your ad and buys a course on your online school, you will then know this person came through the add.
It will tell you that you have now 1 conversion through this add!