The 40 A rated current (In) and 300 mA rated residual current (IΔn) at 230 V AC, 50 Hz define its core protection envelope: it will disconnect the circuit when leakage to ground exceeds 300 mA, while carrying up to 40 A of load current continuously. The 1 kA surge current resistance (IΔm) tells you it can withstand the inrush from a nearby lightning strike or switching transient without welding its contacts shut — important for panels fed from overhead lines or in industrial zones with heavy switching gear.
The N-left variant means the neutral terminal is on the left side of the device — check your busbar arrangement for the panel layout. Terminals accept 1 to 16 mm² solid or stranded conductors with a tightening torque of 2.5 to 3 N·m.