If you do not already know what it is, Google Lens can identify a number of items that we use or come across on a daily basis, and then tell you more about these objects.
For example, if you were to point the phone camera towards a monument like The Gateway of India, Lens will give you more details about it. Once you open the app, it brings you to a viewfinder. Here, Lens looks to identify nearby objects and then provide you with information.
Earlier, Google did mention that Lens will be built into the default camera apps on “supported devices from LG, Motorola, Xiaomi, Sony Mobile, HMD/Nokia, Transsion, TCL, OnePlus, BQ, Asus, and of course the Google Pixel.”
There aren't any new features in the app though, it works the same way it used to. The only difference is that you have a standalone app now.
Previously, Lens was exclusive to the Pixels, but Google started rolling Lens out widely a few weeks ago.
On Google Play, the app says it requires Android Marshmallow and above. If you want to get the standalone app, it's in the Play Store. However, currently, not many users are able to access the feature.