can my friends use the HomePod

See this article from imore: https://www.imore.com/how-secure-airplay-homepod

Note that you can set it up so that friends can AirPlay to your HomePod even if they aren't on your local wifi. If you're using that setting, you might well want to consider a password. But if they're on your local network, I believe they can AirPlay to it just as you can.

Hello,

You can put a password on the HomePod so if they are on the same network as the HomePod is on they can find it in the Airplay menu and will be asked to enter a password.

Hope this helps,

Kaan