For the QB Desktop program:

Basically you just take the installer CD/file and install it on the next machine and make the appropriate selections from the prompts.  If you dont have the original installer you can download it (if its still a 'current program)

But - you need to be very clear on what you are trying to achieve:

Are you just setting it up so you (single user) have an alternate workstation?

or are you moving from a single user setup to a simultaneous multi-user setup? 

Either way both locations have to be on the same LAN - but the setup steps are slightly different.

and you must have the original license key regardless