Google has added a way to put a password on your Web and Activity page, which shows all your activity from across Google services, including your searches, YouTube watch history, and Google assistant queries (via Android Police). Without the verification, anyone who picks up a device you’re logged into could see that activity.
To activate the verification, you can go to activity.google.com, and click the Manage My Activity verification link. From there, you can select the Require Extra Verification option, save, and enter your password to confirm that you’re the one trying to make the change.
If you don’t have the verification turned on, visiting activity.google.com will show a stream of your Google activity from across your devices, without asking for a password.
Turning on verification, however, will require whoever’s trying to see the information to click the Verify button and enter the Google account password before it’ll show any history. For those who share a computer, or who sometimes lets others who aren’t exactly trustworthy use their device, this could be a very useful toggle.
While you’re on the Web and App Activity page, you can also take a look at what activity Google is saving, and whether it’s being auto-deleted. Then, you can decide if you’re happy with those settings. If not, this is the page to change them.