Hello there, Fred9527.
It sounds like you're have questions on what setup is needed for a particular output from your Epson projector when using your Mac. For a good general help on troubleshooting display issues with your MacBook Pro, the following Knowledge Base article is a great place to start:
Get help with video issues on external displays connected to your Mac
Additionally, Epson has some great resources on their support site. The following link is support for El Capitan specifically and Epson's devices:
OS X El Capitan Support - Epson America Inc.
This video on their site also provides a great overview of connecting your device to your Apple computer:
Epson Video Library - How to Connect to an Epson Projector
If you are looking for more specific information, you may find more detailed information by searching with the Model of projector you have.
Thanks for reaching out to Apple Support Communities.
Kind Regards.