Learn Italian: Lavoro al quinto piano. - I work on the fifth floor.

In Italian, ordinal numbers like quinto (fifth) usually come before the noun they describe, just like in English. This is a helpful exception to remember, because most regular descriptive adjectives in Italian go after the noun.

Why does quinto end in -o?

Ordinal numbers act like adjectives, so their endings must change to match the gender and number of the noun they belong to. Because piano (floor) is a masculine singular noun, quinto uses the masculine singular ending -o.

Why does this sentence use al instead of a word for 'on'?

In English, we say we work 'on' a floor, but Italian uses the preposition a (at/to) for the floors of a building. Here, a combines with the masculine word for 'the' (il) to become the combined word al.

Doesn't piano mean 'slowly' or refer to the musical instrument?

Yes, piano is a very common word with multiple meanings! Depending on the context, it can mean 'softly' or 'slowly', a 'plan', the musical instrument (short for pianoforte), or, as in this sentence, a 'floor' or 'level' of a building.