Bi runs on your machine and opens the workbench in your browser. It does not connect to a Bi server — there is no such server.
How it runs
On launch, Bi starts a local service and the UI talks to it through the browser. Think of it as a small application that only runs on your computer, with data stored locally.
Who can reach it
By default, a browser on the same machine can reach it. Bear in mind who else might: other devices on the same LAN and other programs on your machine may be able to access the address.
For that reason, do not expose it on an untrusted network. If you need to restrict access, use the system firewall or narrow the listening scope.
Port
The UI port can be changed in Settings. If the default is taken, choose another.
Security note
Treat it as a local application, not as a security barrier for serving others.