CRJ-900 First Officer reported inadvertently descending below final approach fix altitude before the fix and not recognizing the low altitude until the 1;000" call by the radar altimeter."

Narrative

Got too low on visual approach to Runway XX in ZZZ. Lost situational awareness during visual approach backed up by the ILS. Intercepted the LOC above the ILS FAF altitude. Began descent to the FAF altitude but altitude selector was mistakenly set below the FAF altitude. As a result the decent continued below the FAF altitude while still outside the FAF. Flight crew was alerted to the situation buy the '1000' call by the radar altimeter. Upon recognition of this the autopilot was disconnected and a climb was performed to the appropriate altitude. The glide slope was intercepted and a normal landing was performed. Actual minimum altitude is unknown but I estimate approximately 900 AGL. Debrief was performed after shutdown at the gate.First Officer (FO) inexperience and an incorrect setting of the altitude selector compounded by low time Captain (CA) and momentary high workload.Perhaps more emphasis during simulator training on flying visual approaches in outstations with less that ideal ATC vectoring/ altitude management leading up to the approach.