FPR maintains pressure in the rail at a certain spec.
Fuel Pressure Regulator - General Information and Replacement
The damper keeps that pressure from changing with every little pulse from the fuel pump. Think like a surge protector. Both work in unison to maintain an even pressure for the injectors.
The intake vacuum is supplied to both, and the changing pressure (which is tied to RPMs) changes the spec of each one as the needs for the fuel pressure change across the RPM range.
The 944 has one FPR and one damper.