It's the piece that sits between the contactor and the motor — when the motor pulls too much current for too long, the bimetal strip heats up and trips the auxiliary contact, dropping out the coil. The note on this variant says "Tripped," which is the message the relay sends back to the PLC or indicator light when it's done its job.
Mounting is straight contactor-mount — no DIN rail needed, it snaps onto the bottom of the matching contactor (3RT5036 frame). The screw-type terminals on the main circuit accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire. The auxiliary switch is integrated, so you get one N/C and one N/O contact built in. The Pozidriv PZ 2 screwdriver tip is what you want on the van for the terminal screws.
The auxiliary contact ratings cover a wide control-voltage range: 2 A at 24 V, 0.3 A at 60 V, 0.22 A at 110 V, 3 A at 120 V, 0.22 A at 125 V, 0.11 A at 220 V, 2 A at 230 V, and 1 A at 400 V. That's enough to switch most PLC inputs, relay coils, and indicator lamps directly — no intermediate relay needed for most 24 VDC or 120 VAC circuits.