Learn Hardcore Russian: Мой отец работает в офисе.

отец – more formal, neutral, “father”.
Often used in documents, official speech, and more formal contexts.
папа – more informal, emotional, “dad / daddy”.
Common in everyday family speech, especially by children.

Your sentence could also be:

Мой папа работает в офисе. – My dad works in an office.

Same grammar, just a different level of formality.

Why is there no word for “a” or “the” in this sentence?

Russian does not have articles like a / an / the. The noun офисе stands on its own, and context tells you whether to understand it as “an office” or “the office”.

So Мой отец работает в офисе can mean:

My father works in an office (just describing the type of place)
My father works in the office (if both speakers know which office)

If you really need to specify, Russian uses other words:

в этом офисе – in this office
в одном офисе – in one (some) office

What exactly is работает? How is it formed from работать?

Работает is the 3rd person singular, present tense form of the verb работать (to work).

Infinitive: работать – to work
Present tense forms:

я работаю – I work / I am working
ты работаешь – you (sg., informal) work
он / она / оно работает – he / she / it works
мы работаем – we work
вы работаете – you (pl. or formal) work
они работают – they work

Since мой отец = he, you need работает.

Also, работать is imperfective, so it describes an ongoing or habitual action (he works / is working), not a single completed event.

Why can’t I say Мой отец работа в офисе?

Because работа and работает are different parts of speech:

работа – noun: work, job
(My father work in the office – incorrect in English too)
работает – verb: works / is working

Russian, like English, needs a finite verb to make a normal sentence with a subject and a predicate. So you must use работает, not работа:

✅ Мой отец работает в офисе.
❌ Мой отец работа в офисе. (ungrammatical)

Can I change the word order, for example Мой отец в офисе работает or В офисе работает мой отец?

Yes, but the emphasis changes.

Мой отец работает в офисе.
Neutral, basic word order (Subject–Verb–Place). Simple statement.
Мой отец в офисе работает.
Sounds a bit unusual in isolation; can emphasize “in the office (not somewhere else)”.
В офисе работает мой отец.
Emphasizes кто? – who works in the office.
Roughly: It’s my father who works in the office (not someone else).

Russian allows relatively free word order, but the most natural and neutral version here is:

Мой отец работает в офисе.

Why is it в офисе and not в офис?

Because в + prepositional case is used for location (where?), while в + accusative is used for direction (where to?).

в офисе (prepositional) – in the office → answer to где? (where?)
в офис (accusative) – to the office / into the office → answer to куда? (where to?)

Your sentence describes where your father works (his location), not movement, so you use:

в офисе, not в офис.

What case is офисе, and how do I know to use -е here?

Офисе is in the prepositional case, singular.

Pattern for a regular masculine noun like офис:

Nom.: офис
Gen.: офиса
Dat.: офису
Acc.: офис
Instr.: офисом
Prep.: (в / о) офисе

When you use в to indicate location (in/at a place), you generally use the prepositional case:

в офисе – in the office
в школе – at school
в магазине – in the shop

So -е here is the standard prepositional singular ending.

Do I always need to say мой, or can I just say Отец работает в офисе?

You can say:

Отец работает в офисе.

This is grammatically correct. In Russian, with close relatives (мама, папа, отец, мать, брат, сестра), the possessive мой / моя is often omitted when it’s obvious you mean your own family member.

Differences:

Мой отец работает в офисе. – neutral, a bit more explicit: My father…
Отец работает в офисе. – often understood as My father works in an office, if context is clear.

If there is any ambiguity (e.g. you might be talking about someone else’s father), using мой is safer.

How do I pronounce this sentence correctly? Where is the stress?

Stresses:

Мой – one syllable, [мой]
отец – stress on -ец: оте́ц
работает – stress on the second syllable: рабо́тает
в офисе – о́фисе, stress on the first о

Approximate pronunciation (Latin letters):

Мой отец работает в офисе.
→ Moy a-TYÉTS ra-BÓ-ta-yet v Ó-fi-sye

Notes:

Unstressed о often sounds like a in normal speech, so рабо́тает is closer to rɐ-BO-ta-yet.
In в офисе, the в is usually clearly pronounced: v Ó-fi-sye.

What’s the difference between в офисе and на работе?

Both can translate as “at work”, but they focus on different things:

в офисе – literally “in the office (building)”.
Emphasizes the physical place: an office as a type of workplace.
на работе – literally “at (his) work / at his job”.
Emphasizes the state of being at work, not necessarily in an office (could be a factory, shop, hospital, etc.).

Examples:

Мой отец работает в офисе. – His job is office work; his workplace is an office.
Моего отца сейчас нет дома, он на работе. – My father isn’t home now; he is at work (wherever that is).

How would this sentence look in the past and future tenses?

Base (present):

Мой отец работает в офисе. – My father works / is working in an office.

Past tense (masculine):

Мой отец работал в офисе. – My father worked / used to work / was working in an office.

Future (imperfective, “will be working / will work regularly”):

Мой отец будет работать в офисе. – My father will work / will be working in an office.

(There is also a future with a perfective verb, e.g. поработает, but that adds a nuance like “will work for a while / for some time,” not just a neutral future job description.)