It carries a 100 kA breaking capacity at 400 V AC (and at 240 V, 500 V, and 690 V AC as well), so it can interrupt severe faults without upstream fuses needing to clear first. Mounts on a 35 mm DIN rail (DIN EN 60715) with a screw-and-snap-on mechanism — no tools needed for the snap, but the screw terminal connections for the main circuit take an M4 screw and accept 2×(1...2.5 mm²) or 2×(2.5...10 mm²) solid or stranded wire. The S0 frame size keeps the footprint tight at 97 mm deep, 45 mm wide, 97 mm tall, with 50 mm clearance needed above and below for arc venting, and 30 mm at the sides.
The 100 kA breaking capacity at 400 V AC (and at 240 V, 500 V, and 690 V AC) means this breaker can safely interrupt a fault current up to 100,000 amps without the arc escaping or the device rupturing — that's high enough for most industrial transformer secondary circuits fed from a large distribution transformer. The gL/gG fuse backup rating at 690 V is 4 A, which tells you the maximum fuse size that can be used upstream for coordination.