Google had announced at the I/O 2018 Conference that the visual search feature will be coming soon to the third party camera Apps. Now, the company has made this feature available on the Google camera App in Pixel and Pixel 2 phones.
Google Lens is already available in the navigation drawer as the second to last menu item, just above settings. While on the Camera App, it is a simple option just like the AR Stickers, Portrait, or Slow Motion. Once you open the Lens option, you can tap anywhere on the screen to begin a search.
You can download the updated Camera app via the Google Play Store.