If you install and run Unreal Engine on a Mac without having installed Apple's XCode toolset first, you'll get an error stating that Unreal can't find XCode install the first time you try to launch the Engine.
This video is a quick tutorial on fixing this error by installing XCode (free) from Apple on the App Store, and accepting the license agreement.
Chapters in this video:
00:00 Unreal Can't Find XCode Install...
00:18 Launch Apple's App Store
00:25 Find, & Install XCode Free from Apple
00:42 Open & Accept Apple's License Agreement
00:53 Quit XCode Install & Run Unreal
00:00 Unreal Can't Find XCode Install...
00:18 Launch Apple's App Store
00:25 Find, & Install XCode Free from Apple
00:42 Open & Accept Apple's License Aggreement
00:53 Quit Xcode Install & Run Unreal