Een inwoner fietst in het park.

Here, een means a/an.

So:

• een inwoner = a resident

Dutch een can also mean one, but in a sentence like this it is normally just the indefinite article, like English a.

Inwoner means resident or inhabitant.

It is a singular noun:

• de inwoner = the resident
• een inwoner = a resident

It refers to someone who lives in a particular town, city, or country.

Because fietst is the conjugated form of the verb fietsen, meaning to cycle or to ride a bike.

The subject is een inwoner, which is third-person singular, so Dutch uses:

• ik fiets = I cycle
• jij fietst = you cycle
• hij/zij/het fietst = he/she/it cycles

Since een inwoner is like he/she/a resident, the correct form is fietst.

Yes. Fietsen is the normal Dutch verb for to cycle, to bike, or to ride a bicycle.

Dutch often uses this single verb where English might say:

• to bike
• to cycle
• to ride a bike

So Een inwoner fietst simply means A resident is cycling / cycles.

This is the standard Dutch word order for a simple main clause:

subject + verb + other information

So:

• Een inwoner = subject
• fietst = verb
• in het park = prepositional phrase telling where

This is very similar to normal English word order:

• A resident cycles in the park.

In het park means in the park.

• in = in
• het = the
• park = park

The noun park is a het-word in Dutch, so its definite article is het, not de.

That is why you say:

• het park = the park

and not:

• de park

Dutch often uses the simple present tense where English might use either:

• cycles
• is cycling

So Een inwoner fietst in het park can often be understood as:

• A resident cycles in the park
• A resident is cycling in the park

Dutch does have ways to emphasize an ongoing action, but in a basic sentence the simple present is very common.

Yes, it can.

Depending on context, it could mean:

• A resident cycles in the park (general/habitual)
• A resident is cycling in the park (happening now)

Dutch present tense often covers both meanings, so context tells you which one is intended.

It is a de-word:

• de inwoner = the resident

There is no perfect rule that lets you always predict whether a noun takes de or het, so this often has to be learned with the noun itself.

A useful habit is to learn nouns together with their article:

• de inwoner
• het park

Yes, in is the natural choice here.

• in het park = in the park

It means the cycling takes place inside the area of the park.

Sometimes Dutch uses different prepositions from English in other expressions, but here in matches English very closely.

A rough pronunciation is:

• fietst ≈ feets-t

A few helpful points:

• ie in Dutch sounds like English ee in see
• the final st is pronounced
• Dutch f is like English f

So fietst is one syllable, compact and crisp.

You could say:

Inwoners fietsen in het park. = Residents cycle / are cycling in the park.

Changes:

• Een inwoner → Inwoners
• fietst → fietsen

That is because the subject becomes plural, so the verb changes too.

Yes.

That would mean:

• De inwoner fietst in het park. = The resident is cycling / cycles in the park.

The difference is:

• een inwoner = a resident, any one resident
• de inwoner = the resident, a specific one already known from context