Powiedziałem to wczoraj w biurze.

I said that yesterday in the office.

Breakdown of Powiedziałem to wczoraj w biurze.

• ja: I
• w: in
• biuro: the office
• wczoraj: yesterday

Questions & Answers about Powiedziałem to wczoraj w biurze.

What’s the difference between powiedziałem and mówiłem?

powiedziałem is the past tense of the perfective verb powiedzieć (“to say/utter once”), so it describes a completed action (“I said it”).
mówiłem is the past tense of the imperfective verb mówić (“to be speaking/talking over a period of time”), used for ongoing or repeated actions (“I was saying” or “I used to say”).

Why does powiedziałem end in -em?

The ending -em marks first-person singular (I) in the masculine past tense of perfective verbs.
If the speaker were female, it would be powiedziałam (ending -am).

How would a female speaker say this sentence?

A woman would change the verb ending to feminine:
Powiedziałam to wczoraj w biurze.

What does to mean here, and why is it used?

to is the neuter singular direct-object pronoun “it.” It stands for whatever “thing” was said. In Polish, the accusative neuter form of to is the same as the nominative, so it stays to.

What case is w biurze, and why is it used?