Hello,
At the moment only a PC version of The Sims 4, via Origin, has been announced. This will not be compatible with Mac. The only way to possibly play The Sims 4 on a Mac was to setup Bootcamp or a Parallels desktop with a full license of Windows 7 or 8 (however this is yet to be confirmed).
If you do choose to use one of the options mentioned above, the process is you buy the game online at the EA Origin store, then download the Origin program. After logging in, you should find The Sims 4 in your Origin library of games, where you can then download and install the game.
I hope this helps and keep simming,
Cody
