No it usually works like this:

1. Plug in/turn on your smart device (light bulb, temperature sensor, etc)
2. Open a smart home app on your phone (Apple and Google both include one in the OS, or you can use third party apps)
3. Click "add device"
4. It'll pop up a QR code scanner, scan the QR code that came with the device

Once scanned, it will do whatever is necessary to connect the device to your home network.

It's a flexible system that can use a variety of network technologies... (wifi, ethernet, bluetooth, thread, ultra wideband, etc). It will pick the best one available. And switch technologies automatically if one of them becomes unavailable.

Thread has about the same range as wifi, but it uses a lot less power. It doesn't really have enough bandwidth for something like a video camera, but it's great for light bulbs, temperature sensors, etc.