Something that's spotless is extremely clean, like your spotless new sneakers without a single smudge on them (yet).
A spotless floor looks exactly the way it sounds—so clean that there's not a single spot of dirt or grime on it. You can also use this adjective in a figurative way, to mean "innocent or unimpeachable," like your spotless report card with all As, or your dad's spotless driving record without even a single speeding ticket.