I just purchased the Nest. I set it up at a friend's house & it worked great. I took it home & it won't connect to my wifi? Does it need to be set up all over again, or should it automatically connect since my phone is connected to my wifi?
When you set up your Google Nest device at your friend's house, since your phone was connected to their Wi-Fi network during the install, the Google Nest install process would have configured your Google Nest device with your friend's Wi-Fi network name (SSID) and password. You will need to re-configure your Google Nest device with your own Wi-Fi network's credentials. You might also need to factory reset your device and set it up again in order to reconnect it.
How this is done depends on what Google Nest device you have (your post just says "the Nest"), and it can be challenging. See this Google Nest Help page:
One other complication to consider is whether you also happened to connect to your friend's Google Nest "home" (if they have one) and connected it to their "home". If so, you'll have to remove the device from their "home" and create your own "home" and add it there.
From another Google Nest customer.
I'm dropping by to ensure that everything is covered here. I hope that sheds some light on the issue. If you have other questions and concerns, feel free to let me know.
Thanks for your help here, MplsCustomer.