The 4.5 kA breaking capacity at 400 V AC (per EN 60898) tells you this MCB can safely interrupt a fault current up to 4.5 kA without welding its contacts or failing open; that is sufficient for most residential and light commercial sub-distribution boards, but if your fault current at the panel exceeds 4.5 kA you need the higher-rated 5SL4363-7 sibling (10 kA). Single-phase operation is rated at 250 V AC. The DC rating tops out at 72 V — so this is primarily an AC device; do not spec it for a 110 V DC string unless you stay under that ceiling.
The 3 MW width (54 mm) means it occupies three adjacent 18 mm slots — check your rail fill before committing. That is adequate for a distribution breaker that cycles infrequently; if your design calls for frequent switching (e.g., a load-shedding contactor), this is not the part for that duty.