Although the Xbox app is available on ios, it is not yet available on the mac. To use the app on your Mac, you need to install windows 10. To this, you will have to either make a partition on your Mac hard drive or run the OS through a virtual machine.
Other than that, your mac specs need to be good to run the Xbox app. The following steps will allow you to use Xbox app on your mac:
Install Windows 10 and head to the Windows Store app
Sign in to the Windows Store app
Search for Xbox
Download the application and sign in to your Xbox Live account that you wish to use
After you sign in, you will be presented with your Microsoft activity feed
Through the Xbox app, you will be able to use all Xbox features on your Mac device. This includes chatting with your friends as well.