I have Roon core on a music server.and would like to make my Mac computer an endpoint.mHow do I do that.My computer has ROON installed on it.
I’m also new to all the Roon Stuff. But can’t you just install the RoonBridge on your Mac? I think that’ll do the trick 
If your Mac has Roon on it then it already is an endpoint.
Indeed. If you install the Roon main software, it will install the core and the endpoint. If you would install the same software on a second computer in your LAN, you are offered a choice between installing a second Roon core (you probably don’t want that), or and endpoint with remote controls and album screens that connects to the existing Roon core.
Using your second computer you need to switch zones as detailed in Knowledge Base / User Guide / switching Zones
https://kb.roonlabs.com/Zone