In Xcode, choose File/New... Project.
From the template chooser, select macOS, Application, Command Line Tool. Click Next
give it a name (maybe "hello")
choose C++ from the language popup
click Next
choose where to save your project
Xcode will open the project and it will have a starter main() routine.
Xcode help is here https://developer.apple.com/documentation/xcode
This will get you started. After that, this forum, and the Internet in general, is your friend.
Most of the differences between Mac and Windows are in the application and system frameworks and APIs. But you'll face an uphill struggle with programming on the Mac if you insist on using C++, because most of the APIs are Objective C or Swift, and some of the new frameworks are Swift-only.