Typically it's just install the drivers software and then set the preferences in Reason under the audio tab so that the M-Box is selected as your device.
Are you struggling with this part? If so then re-installing drivers and checking the cabling/ports is the first things you should try.
If it's not this, then please give us some idea of the problem that you're having.
"I decided to call my music 'organized sound' and myself, not a musician but 'a worker in rhythms, frequencies, and intensities'”
Edgard Varèse 1962