Curve K means the magnetic trip operates between 8 and 12 times rated current (504–756 A), designed for inductive loads like motors and transformers where inrush is brief but high; it avoids nuisance trips that a B-curve or C-curve would cause on those starts.
The 3-pole block occupies three modular-width positions (about 52.5 mm total). Wire termination accepts conductors up to 25 mm², which matches the 63 A rating for a motor branch circuit or transformer primary protection. I'd land the line and load conductors with ring lugs and torque to the terminal marking; the spring-cage variant (if present) wants ferruled stranded for a clean pull.