Learn Hardcore Greek: Χτες δούλεψα πολύ στο γραφείο.

It means yesterday.
Common variants you’ll see: χτες, χθες (slightly more formal), εχτές, εχθές. All are correct and understood.
Pronunciation tip: χ is like the German sound in Bach; χτες sounds like [xtes]. One‑syllable χτες/χθες normally has no accent mark; εχτές/εχθές carries the accent on the last syllable.

Why is there no “I” in the sentence?

Greek is a “pro‑drop” language. The verb ending already tells you the subject. δούλεψα is 1st person singular, so it means I worked. You only add εγώ for emphasis or contrast: Εγώ χτες δούλεψα πολύ…

What tense is δούλεψα, and how is it different from δούλευα?

δούλεψα is the aorist (simple past): a completed action in the past (Yesterday I worked).
δούλευα is the imperfect: an ongoing or habitual past action (Yesterday I was working / I used to work).
Greek past tenses are about aspect (completed vs ongoing), not just time.

How is δούλεψα formed from δουλεύω?

Base verb: δουλεύω (I work).
Aorist (simple past) stem: δούλεψ-
- endings → δούλεψα (I worked).
Full aorist active: δούλεψα, δούλεψες, δούλεψε, δουλέψαμε, δουλέψατε, δούλεψαν/δουλέψανε.
Notes:
- Stress shifts compared to the present: δου-ΛΕ-ω vs ΔΟΥ-λε-ψα.
- Many aorists use -ψα/-ξα (e.g., γράφω > έγραψα). Not every verb takes a visible έ- prefix, as you see with δούλεψα.

What does πολύ mean here? Is it the same as πολλή/πολλοί/πολλά?

Here πολύ is an adverb meaning a lot / very much; it modifies the verb.
As an adverb, πολύ does not change form.
The forms πολύς (masc.), πολλή (fem.), πολύ (neut.) are adjectives meaning much/many and agree with a noun: πολλή δουλειά (a lot of work), πολλοί άνθρωποι (many people).
Spelling tip: adverb πολύ has one λ; the adjective forms πολλ- have double λ.

Does πολύ here also mean “hard,” as in “I worked hard”?

Often yes, by implication. Δούλεψα πολύ can mean I worked a lot / I worked hard. If you want to be explicit, use σκληρά: Δούλεψα σκληρά.

Where should πολύ go in the sentence? Can I put it before the verb?

Neutral placement: after the verb → Δούλεψα πολύ…
You can move it, but it’s less common: Δούλεψα στο γραφείο πολύ.
Πολύ δούλεψα… is possible for emphasis but sounds marked. Default to after-verb placement.

What does στο mean exactly?

στο = σε (in/at/to) + το (the, neuter sg.). It’s a contraction.
Other common contractions: στον (σε + τον, masc.), στη/στην (σε + τη(ν), fem.).
After σε, the noun is in the accusative case.

Does στο γραφείο mean “at the office” or “at/on the desk”?

γραφείο can mean office or desk.
στο γραφείο most commonly means at the office (workplace).
To clearly mean the furniture, say πάνω στο γραφείο (on the desk) or στο γραφείο μου (at my desk), depending on context.

What case is γραφείο here, and why does it look the same?

It’s neuter singular accusative after σε: (σε) το γραφείο → στο γραφείο.
Neuter nominative and accusative singular have the same form (το γραφείο), so it looks unchanged.
Plural: τα γραφεία.

Is the word order fixed? Can I move χτες?

Greek word order is flexible. All of these are natural, with slight changes in emphasis:

Χτες δούλεψα πολύ στο γραφείο.
Δούλεψα πολύ χτες στο γραφείο.
Δούλεψα πολύ στο γραφείο χτες. Starting with the time word (χτες) is very common.

How do I pronounce each word?

Χτες: [xtes] — χ like in Bach; the cluster χτ = [xt].
δούλεψα: [ˈðu.le.psa] — δ like English “th” in this; ου = “oo”; ψ = “ps”; stress on the first syllable.
πολύ: [poˈli] — stress on the last syllable.
στο: [sto].
γραφείο: [ɣraˈfio] — γ is a soft “gh” [ɣ]; ει = “ee”; stress on -φεί- (gra-FEE-o).

How do I say “I didn’t work much yesterday at the office”?

Δεν δούλεψα πολύ χτες στο γραφείο.

δεν
- verb makes the negation.
With negation, πολύ is understood as much.

How can I change the place to say where I worked?

Replace the place phrase:

στο σπίτι = at home.
από το σπίτι = from home (work from home): Χτες δούλεψα πολύ από το σπίτι.
στη δουλειά = at work.
στο πανεπιστήμιο = at the university.