I confess I have no idea how they work with wifi, since it didn't require any passwords etc. but work they do.
How it seems to work on a regular domestic WiFi setup is this:
On the phone app, when you search for a new speaker, it initially connects over bluetooth.
It has to do this, since the speaker doesn't know the passwords to your WiFi.
The App then scrapes the WiFi connection details from the phone, and sends them over to the speaker via Bluetooth.
The speaker then connects to WiFi, and the connection then transfers to WiFi.
When we then moved the system to Feanor Towers, the WiFi connection was no longer found, but the app found the Boost, and set it up. It then used the Boost to search for speakers, and it found them. So the speakers seemed to magically connect to the Boost's hidden network with no user configuration required.