Maintenance for the week of October 6:
• [COMPLETE] ESO Store and Account System for maintenance – October 7, 6:00AM EDT (10:00 UTC) - 4:00PM EDT (20:00 UTC)
Can't look at the moment, but from the top of my head:
game files are in /Applications/The Elder Scrolls Online
(append "EU" for, well, the EU client)
settings files and screen shots are in /Users/<account name>/Documents/The Elder Scrolls Online
HTH
P.S.: If you meant how to get the game's installer for Mac, log into your account with Zenimax at https://account.elderscrollsonline.com/. If you have Early Access, the links for PC and Mac clients should be in the "Purchased Games" section.