The 15 A rating means it protects a branch circuit carrying up to 15 A continuous; the 6 kA interrupting capacity at 277 VAC (10 kA at 250 VDC) tells you it can safely clear a fault up to that level without welding contacts or cascading upstream. DIN-rail mount, so it clips into any standard 35 mm rail in a panel or enclosure.
Single-pole width (roughly 18 mm per pole) — fits a compact sub-panel or a crowded enclosure. Rated 277 VAC line-to-neutral or 250 VDC; verify the supply voltage and fault current available at the panel before specifying. The K-curve magnetic trip holds through motor inrush without nuisance tripping, but coordination with downstream loads should be checked if the circuit feeds a soft-start or VFD.