You need to create/edit an OGM to run the plugin (OGM Properties, Advanced tab).
Browse and select the fax plugins exe file. As noted in the fax.txt file with the plugin the first argument in the phonenumber you want it faxed to and the second in the filename. Unlesss you want a constant number you may need to consider using an input variable in the OGM to get the users toi input their fax number. In the case the first argument would be something like %number% (whatever you chose in the data entry section.
Remember to tick 'Is IVM process' on the dialogue where you add the plugin.
IVM Phone Answering Attendant Software