How do I connect my Mac to the BT home hub?

You would normally connect via WiFi and enter the correct password. I believe the default initial password is printed on a sticker on the BT HomeHub.

Note: Once you have it working you should change both the admin password and the WiFi password from the default as a security measure.

However alternatively the BT HomeHub also has several Ethernet sockets and you could therefore connect the Mac via an Ethernet cable.

Your message is unclear but gives a very subtle impression that rather than wanting to know how you are actually having a problem doing so. If so it would help to have a bit more information such as any error messages or symptoms, and what steps you have tried. Are any other devices successfully connecting?

Based on experience with some BT Hubs and other ISP provided routers, if the router has no Internet connection it will typically fail to provide an IP address to clients.

I would connect a computer via Ethernet and if it still cannot access the Internet try accessing the management webpage for the router, then see what connection status it reports. The admin password is usually on a sticker on the router, or maybe on a piece of paper in the router box.

System preferences > Network > Wi-Fi > (assist me) > (diagnostics)