Learn Hardcore Polish: Wieczorem oglądamy razem ulubiony serial w telewizji. - In the evening we watch our favourite TV series together.

Wieczorem is the instrumental form of wieczór (evening) used adverbially to mean in the evening.
Polish very often uses bare case forms (no preposition) to express when something happens:

Rano – in the morning
Po południu – in the afternoon
Nocą – at night

So Wieczorem oglądamy… literally feels like “(During) evening we watch…”.
W wieczorze would sound odd in this context and is practically never used in everyday Polish.

What grammatical form is oglądamy, and why is there no pronoun like my?

Oglądamy is the 1st person plural, present tense, imperfective form of the verb oglądać (to watch). It already encodes “we” in its ending -my.

In Polish, subject pronouns (ja, ty, my, wy etc.) are usually dropped, because the verb ending shows who is doing the action.
You can say My oglądamy…, but that is used for emphasis, like “We (as opposed to others) are watching…”.

What is the difference between oglądać and obejrzeć? Could I say obejrzymy instead of oglądamy?

Oglądać is imperfective – it describes an ongoing, habitual, or repeated action:
Wieczorem oglądamy… = we (usually / regularly) watch in the evening, or we are watching (this evening).

Obejrzeć is perfective – it focuses on the completed whole of the action.
Wieczorem obejrzymy ulubiony serial = We will (finish) watching our favourite series this evening.

So oglądamy = happening now / generally;
obejrzymy = completed future event.

Why is razem placed after oglądamy? Could I say Razem oglądamy… instead?

Both Oglądamy razem ulubiony serial and Razem oglądamy ulubiony serial are correct.

Polish word order is fairly flexible. The neutral choice is often Subject – Verb – other elements, so oglądamy razem… feels natural.
Putting razem at the beginning (Razem oglądamy…) slightly emphasizes together, similar to saying “Together we watch…” in English. The basic meaning stays the same.

Why does the adjective ulubiony come before serial? Could it come after?

In Polish, adjectives normally come before nouns, unlike in some other languages:

ulubiony serial – favourite series
nowy samochód – new car
dobra książka – good book

So ulubiony serial is the standard order.
Adjectives after nouns are rare and usually have a very special, stylistic, or fixed-phrase function. So you should learn the pattern: adjective + noun.

What case is ulubiony serial in, and why does it look like the basic dictionary form?

Ulubiony serial is in the accusative case, because it is the direct object of the verb oglądamy (we watch what? → ulubiony serial).

For masculine inanimate nouns like serial, the accusative singular is identical to the nominative singular:

nominative: serial (as in Ten serial jest ciekawy. – This series is interesting.)
accusative: serial (as in Oglądam serial. – I watch a series.)

The adjective ulubiony agrees with serial in gender, number and case (masculine, singular, accusative), and in this combination the form is also ulubiony.

Why is there no word like “the” before ulubiony serial? How do I know if it is “a favourite series” or “the favourite series”?

Polish has no articles (no equivalents of a / an / the).
The bare phrase ulubiony serial can correspond to:

“a favourite series”
“the favourite series”
“our favourite series”, depending on context.

In this sentence, everyday context and the adjective ulubiony make it natural to understand it as “our favourite series” or “the favourite series (we always watch)”.
Polish relies on context and word choice, not on articles, to express this kind of nuance.

Why do we say w telewizji, not na telewizji or w telewizorze?

In this sentence, w telewizji means “on TV / on television” as a medium of broadcasting.
The preposition w + locative (w telewizji) is the standard way to say “on (the) television” in this abstract, media sense:

Leciało to w telewizji. – It was on TV.

Na telewizji would sound like “on top of the TV set” (physically sitting on it), so it is wrong here.
W telewizorze would literally be “inside the TV set” and is also not used in this context.

What case is telewizji, and how is it formed?

Telewizji is in the locative singular case, used after many prepositions, including w (in) and o (about) when they refer to location or topic.

The nominative (dictionary form) is telewizja.
For many feminine nouns ending in -a, the locative singular ends in -i or -y:

telewizja → w telewizji
szkoła → w szkole
kawa → w kawie

So w telewizji literally means “in television (as a medium)”.

Can I move the time expression Wieczorem to another place, like Oglądamy wieczorem razem ulubiony serial w telewizji?

Yes. Time adverbs like wieczorem are quite flexible in Polish word order. Common options include:

Wieczorem oglądamy razem ulubiony serial w telewizji.
Oglądamy wieczorem razem ulubiony serial w telewizji.
Oglądamy razem ulubiony serial w telewizji wieczorem.

All are grammatically correct.
Putting Wieczorem at the beginning sounds natural and slightly emphasizes when the action happens.

What is the difference between wieczorem and wieczorami?

Both come from wieczór (evening), but:

wieczorem (singular, instrumental) usually refers to a particular evening or this/that evening:
Wieczorem oglądamy serial. – We watch the series in the evening (this evening, or generally, depending on context).
wieczorami (instrumental plural, used adverbially) means in the evenings, suggesting habit / regular repetition:
Wieczorami oglądamy serial. – We watch the series in the evenings (as a habit).

So wieczorami makes the sentence sound more explicitly habitual.

How would the sentence change if the subject were I instead of we?

You would change the verb from oglądamy (we watch) to oglądam (I watch):

Wieczorem oglądam ulubiony serial w telewizji. – In the evening I watch my favourite series on TV.

If you want to emphasize that you watch alone, you can add sam (if you are male) or sama (if you are female):

Wieczorem oglądam sam ulubiony serial w telewizji.
Wieczorem oglądam sama ulubiony serial w telewizji.

How is oglądamy pronounced, and where is the stress? What about wieczorem?

In Polish, stress is almost always on the second-to-last syllable.

oglądamy → o-glą-DA-my
- ą is a nasal vowel; here it sounds roughly like “on” in British “bon” but nasalized (somewhere between “on” and “own”).
- The ł is like English w, but here we have plain l (oglądamy not ogłądamy).
wieczorem → wie-CZO-rem
- cz is like ch in “church”.
- rz (in other words) is pronounced like a voiced “zh” sound, but wieczorem does not contain rz; it has cz only.

Main point: both words have stress on the second-to-last syllable: ogląDAmy, wieCZOrem.

Is there any difference in meaning between serial and program in this context?

Yes.

serial = a series, typically a show with episodes and a continuing story (e.g. dramas, sitcoms, Netflix series).
program (or program telewizyjny) is more general: any TV program / show – it could be news, a quiz show, a documentary, etc.

So ulubiony serial specifically means a favourite TV series, not just any type of television program.