Think of the mini hub as a spare home hub, except this one connects to the 4G mobile network, rather than through your phone line.
It simply requires power to keep the battery charged, just look for available wi-fi networks and the mini hub will show up, connect to it and enter the password supplied with the mini hub.
If your PC is hard wired through an ethernet cable, does your mini hub have the ethernet connection on the back ? older models didn't so you might have to use wi-fi only until your fault is fixed.
Is it a PC you're trying to connect and do you have any other devices like a mobile phone, laptop etc ?
There's also a guide on the BT help pages, click the following text Using the 4G Mini Hub for BT Halo customers