Wi-Fi Assistant was a feature that was available only on Google’s Project Fi cell service, but now it is available on all Nexus devices. Wi-Fi Assistant allows your Nexus mobile phone to access millions of open and free Wi-Fi hotspots helping you cut your mobile data charges and increasing your overall Internet connectivity. Once activated on your Nexus mobile phone, Google’s Wi-Fi Assistance automatically connects to Wi-Fi hotspots that are available around you. According to Google, the Wi-Fi Assistant is available on your Nexus phone if you own a Nexus phone in the US, Canada, Mexico, the UK and Nordic countries.
How to activate Google’s Wi-Fi Assistant on your Nexus phone?
Just go to Android Settings then from their tap on Google and then tap on Networking. In this section you can toggle the Wi-Fi Assistant feature on and off.
Once your Nexus phone is connected via Wi-Fi Assistant you will be able to see a small key icon in the upper corner of your Nexus smartphone. It is the same as the Android’s virtual private network icon but when your Wi-Fi Assistant is connected to one of the Wi-Fi hotspots, it will mean this particular connection. If you don’t want to remain connected to a particular network, just like any other Wi-Fi connection, you can long press the name of the connection and tap “forget”.
This Google support link explains the entire process of activating Wi-Fi Assistant.