Learn Hardcore Polish: Latem najczęściej biegam rano w parku. - In the summer I most often run in the park in the morning.

Plain lato at the beginning (without case ending, like Lato najczęściej biegam…) would be wrong here, because lato as a bare noun is not in the right case for this time expression.

What exactly does najczęściej mean, and how is it different from często?

często means “often”.
najczęściej literally means “the most often”, but very commonly corresponds to “usually / most often / most frequently” in English.

Morphology:

często – often
częściej – more often (comparative)
najczęściej – most often (superlative)

In this sentence:

Latem najczęściej biegam rano w parku.
→ In summer I usually / most often run in the park in the morning.

If you said:

Latem często biegam rano w parku.

it would weaken the frequency: “In summer I often run in the park in the morning”, not necessarily most of the time.

Why is it biegam and not biegnę?

Polish distinguishes habitual / repeated actions from a specific ongoing movement using different verb stems:

biegać – to run (habitually, generally, here and there) → biegam, biegasz, biega…
biec / biec / pobiec – to run (in one specific direction / one occasion) → biegnę, biegniesz…

In this sentence, biegam is used because we are talking about a habit:

Latem najczęściej biegam rano w parku.
→ In summer, I run (habitually) in the park in the morning.

If you said Latem najczęściej biegnę rano w parku, it would sound odd: biegnę suggests “I am (right now) running / heading somewhere”, not a routine or regular activity.

So, for habits: biegam.
For one specific run going on now or planned: biegnę (or a perfective future form).

What tense is biegam here? Does it mean “I run” or “I am running”?

biegam is in the present tense, imperfective aspect.

Polish does not normally distinguish:

I run (simple present, habitual)
and
I am running (present continuous)

biegam can cover both, but context and the choice of verb (habitual biegać vs directional biec) usually make it clear.

In this sentence, adverbs like latem and najczęściej clearly indicate a habitual meaning:

Latem najczęściej biegam rano w parku.
→ “In summer I (usually) run in the park in the morning.”

If you wanted to emphasize “I am running right now”, you’d more naturally say:

Teraz biegnę w parku. – I am running in the park now.
Teraz biegam w parku can also be used, but sounds more like “These days I’ve been running in the park (as a new habit).”

Why is rano used without a preposition? Could I say w rano or something like that?

You cannot say w rano.

rano is already an adverb / time expression meaning “in the morning”. Polish commonly uses bare words (no preposition) for parts of the day:

rano – in the morning
wieczorem – in the evening
w południe – at noon
w nocy – at night (here a preposition is used)

So:

biegam rano – I run in the morning

There is also a near-synonym:

rankiem – in the morning

You could say:

Latem najczęściej biegam rankiem w parku.

Both rano and rankiem are correct; rano is more common and slightly more neutral/colloquial.

Why is it w parku, not w park or na parku?

Several things are happening here:

Preposition: w vs na
- w is typically used for being inside a space (in a room, in a building, in a park):
  - w parku – in the park
- na is often used for surfaces, open areas, some institutions, events, etc.:
  - na ulicy – on the street
  - na stadionie – at the stadium
For park, the standard choice for “in the park” is w parku.
Case ending: w parku
After w (location “in”), Polish uses the locative case.
The noun park (masculine) has the locative singular form parku:
- (Nom.) park – a park
- (Loc.) w parku – in the park

So:

✅ w parku – correct: “in the park”
❌ w park – wrong case, sounds ungrammatical
❌ na parku – wrong preposition in this meaning (could appear only in rare, very specific contexts, not for normal “running in the park”)

What case is parku, and how is park declined?

parku is locative singular.

Declension of park (a regular masculine inanimate noun):

Nominative (who? what?) – park
- To jest duży park. – This is a big park.
Genitive (of whom? of what?) – parku
- Nie ma parku. – There is no park.
Dative (to whom? to what?) – parkowi
- Przyglądam się parkowi. – I’m looking at the park.
Accusative (whom? what?) – park
- Widzę park. – I see a park.
Instrumental (with whom? with what?) – parkiem
- Idę z parkiem (artificial example, rarely needed).
Locative (about whom? about what? / where?) – parku
- Jestem w parku. – I am in the park.
Vocative – parku (rarely addressed directly)

In your sentence, w parku uses the locative to express location: in the park.

Can the word order be different? For example, can I say: Najczęściej latem rano biegam w parku?

Yes, Polish word order is flexible, and several variants are grammatical. However, the naturalness and emphasis change slightly.

Original:

Latem najczęściej biegam rano w parku.
Neutral focus on the time frame (“In summer I usually…”), then the frequency.

Other possible natural orders:

Najczęściej latem biegam rano w parku.
→ Highlights najczęściej a bit more: “Most often, in summer, I run in the park in the morning.”
Najczęściej biegam latem rano w parku.
→ Emphasis on how often you do this; summer and morning are added as extra info.
Latem rano najczęściej biegam w parku.
→ Groups the times together: “In summer, in the morning, I usually run in the park.”

All these are acceptable and would be understood.
The version you gave:

Najczęściej latem rano biegam w parku.

is also grammatical and understandable, though piling najczęściej – latem – rano at the front can sound slightly heavy; many speakers would still consider it fine in casual speech.

Crucially, none of these changes the basic meaning; they just tweak what feels more “in focus” (frequency vs season vs time of day).

Where should najczęściej normally go in the sentence?

The most typical positions for najczęściej are:

Before the verb:
- Latem najczęściej biegam rano w parku.
- Najczęściej biegam latem rano w parku.
This is very common and natural.
At the very beginning:
- Najczęściej latem biegam rano w parku.

Placing najczęściej after the verb is less common and can sound marked:

Latem biegam najczęściej rano w parku. – still possible, but the focus shifts a bit (“When I run in summer, it’s usually in the morning in the park.”)

As a simple rule:
→ Put najczęściej just before the verb or at the start of the sentence for safe, natural-sounding Polish.

How is najczęściej pronounced? The spelling looks difficult.

najczęściej is pronounced approximately:

[nai̯-CHEN-sh-chay] (very rough English-like guide)

More precisely in IPA: [nai̯ˈt͡ʂɛ̃ɕt͡ɕɛj]

Breakdown:

naj- → nai̯ (like nai in “naive”)
cz → t͡ʂ, similar to English “ch” in “chocolate”, but harder and more retroflex
ę before ś is a nasalized e, here often pronounced close to “en”, but not fully; you can approximate as “en”
ś → a soft sh, tongue closer to the teeth (not as hard as English sh).
ć → a soft ch, similar to “tch” in “gotcha”, but palatalized.
-ej → [ɛj], like “ay” in “day”, but shorter.

You don’t need perfect phonetics to be understood. Aim for something close to:

[nai-CHENSH-chay]

and Poles will understand you.

If I remove latem or najczęściej, how does the meaning change?

Yes, removing them changes the meaning:

Without latem:
- Najczęściej biegam rano w parku.
  → “I usually run in the park in the morning.”
  Now this is about your general routine, not limited to summer.
Without najczęściej:
- Latem biegam rano w parku.
  → “In summer I run in the park in the morning.”
  This states a regular fact but doesn’t say how often (could be every day, could be once a week; it just sounds like a consistent pattern).
Without both:
- Biegam rano w parku.
  → “I run in the park in the morning.”
  A general statement of your habit, with no information about the season or frequency beyond “habitual”.

Each added adverb narrows or specifies your habit: when (latem, rano) and how often (najczęściej).