The 25 A rating carries the continuous load; the 15 kA Icu at 400 V certifies it for use in a panel with a fault level up to that value, per IEC 60947-2. Two poles switched together means it opens both line conductors on a single-phase or split-phase circuit, or one phase plus neutral if wired that way.
Snap-on DIN rail mount, standard 18 mm per pole width — two poles occupy 36 mm of rail space. The D25 rating and 15 kA Icu mean this breaker fits in a sub-distribution board or motor control centre where the fault level is calculated and labelled; it's not a branch-circuit device for a 6 kA domestic board.