Turning off website notifications will prevent a lot of unwanted spam and advertising. Website notifications are useful in some situations, but they are widely abused by many websites. I usually advise turning these off entirely, unless you have a good reason and know why you want them.
To block notifications from all sites…
1. Open Chrome.
2. At the top right, click the More menu. It’s the three dots in the upper-right. It looks like this:

3. Near the bottom of that menu, click Settings.

4. In the search bar at the top, type Notifications.
5. Notice the yellow flag is pointing at Site Settings. Click on Site Settings.

6. In the Site Settings menu, notice that the Notifications entry is marked in yellow, about half-way down the page. Click the Notifications entry.

7. To block all notifications, turn off Ask before sending by clicking the blue button.

8. The setting should now show Blocked.
9. That’s it! Close the tab, you are done.

Windows 10 Bonus Tip: Clear the old notifications from Windows.
Click the Notifications icon in the lower-right of your screen, next to the clock. Next, click Clear all notifications.

See this excellent article from MalwareBytes for more details about notifications and instructions to disable them on Firefox, Microsoft Edge, and Opera.
Image Credits: Wikimedia Commons