Learn Polish: Pracuję o dziewiątej.

The dictionary form is pracować (to work). In Polish, verbs ending in -ować belong to a special group. To make the present tense, you drop the -ować and add -uję for "I" (pracuję), -ujesz for "you" (pracujesz), and so on.

I thought the word o meant 'about'. Does it also mean 'at'?

Yes! While o often means "about" (like talking about a book or a movie), when you use it with time on a clock, it means "at". So o dziewiątej means "at nine o'clock".

Why doesn't the sentence use the regular number dziewięć (nine)?

When talking about hours of the day, Polish uses ordinal numbers (first, second, ninth, etc.) instead of regular numbers (one, two, nine). You are literally saying "at the ninth", where the word for "hour" (godzinie) is implied but almost always left out.

Why does the word for ninth (dziewiąta) end in -ej here?

The preposition o for time requires a grammatical form called the Locative case. Since "hour" is a feminine word, you start with the feminine form of the number (dziewiąta). In the Locative case, feminine adjectives and ordinal numbers ending in -a change their ending to -ej.