1. You'll need to download the Babylon exporter installer from the following link: Download Babylon Exporter
2. Once you've successfully installed the correct exporter version, make sure to enable the plugin in your Maya plugin manager.
3. Before exporting your model, make sure you are only using the Maya renderer materials (lambert,phong,phongE,etc.).
4. When you're ready to export, click on the Babylon menu in the top of your window, if you don't see it here make sure you've enabled both "Loaded" and "Auto Load" in your plugin manager. If you still don't see it, try relaunching Maya.
5. Next you can select your export options in the Babylon window. Use the button next to the file name box to set the file path and name for the file. Note that it will export everything in the scene unless "export selection" is checked.
6. You can try experimenting with different export options based on what you need for your situation!