1. The "Fax" part of "Fax Modem" makes no difference - in fact most modems are indeed fax modems - what that means is that as well as functioning as a modem, it also has fax functionality that allows you to send/receive faxes on your computer with the appropriate software.

2. Modems do not plug into the SCSI port - they plug into one of the serial ports. Obviously Macs don't use the same DB-9 or DB-25 connectors for serial that PCs do, they use a MiniDIN-8 connector instead. You'll need either a new cable with a MiniDIN-8 plug on one end, and whatever plug is suitable for the modem on the other end, or an adapter that goes from MiniDIN-8 to whatever plug on the cable that goes into the machine.