Every CurrentClient app, for iPhone, Android, Mac and Windows, is on one page. It works out which download you need, including which build to take for your Mac.
Once you are installed
Sign in with the same email and password you use on the web. Everything syncs across every device you install on.
Say yes when your device asks about notifications and the microphone. Notifications are how the app reaches you about an incoming call or a new text, and the microphone is what lets you take calls on your computer.