Turn off Mac Notification Center — the easy way!
You can read volumes, or just make a single simple no-command-line-needed modification
The Apple website spends about a page and a half telling you how spend your afternoon turning off notifications app-by-app — but doesn’t mention that you can’t turn off system alerts (likely the reason you Googled TURN OFF NOTIFICATIONS in the first place).
If that doesn’t solve things for you, TekRevue’s article on the subject offers a terminal-based solution, but doesn’t make any guarantees of compatibility with the last several updates. This solution also removes all vestiges of the Notification Center, which may not be ideal if you use some of its features.
Instead, I favor the sneaky-but-safe approach.
1) Open System Preferences
2) Choose the Notifications panel
3) Turn on Do Not Disturb mode…from now until forever
This is a completely ‘button-based’ solution, free of scary command lines (or indeed, inscrutable commands entered on the advice of bloggers).
It also allows you the option of viewing your past notifications at any time, without shoving them in your face every ten seconds. And best of all, it’s guaranteed to be compatible with future updates.