Learn Italian: Quella signora lavora alla posta. - That lady works at the post office.

In Italian, when the preposition a (at/to) is followed by a definite article like la (the), they combine into a single word. Since posta is a feminine singular noun, it takes the article la. Combining a + la gives us the articulated preposition alla (at the).

Doesn't posta usually mean mail? Can it mean the building too?

Yes! While posta translates to mail or post, Italians frequently use it as a shorthand for the post office itself. You might also hear l'ufficio postale for the actual building, but saying someone works alla posta is perfectly natural and very common in everyday conversation.

Why is the word for that spelled Quella here?

The word for that changes depending on the gender and the starting letters of the noun it describes. Because signora is a feminine noun that starts with a consonant, we use Quella. If the feminine word started with a vowel, you would use Quell' instead.

Is lavora the regular form for he/she works?