Volim sjediti uz rijeku navečer.

Because Croatian usually doesn’t need a subject pronoun when the verb already shows who is doing the action.

• Volim = I love / I like
• The ending -m tells you it is 1st person singular: I

So Ja volim sjediti uz rijeku navečer is possible, but ja is usually omitted unless you want emphasis.

Volim is the 1st person singular present tense of voljeti = to love / to like.

In this sentence, it means something like:

• I like
• I love
• I enjoy

When followed by an infinitive, it often expresses liking an activity:

• Volim čitati. = I like reading / I like to read.
• Volim sjediti. = I like sitting / I like to sit.

So here it is not necessarily strong romantic love; it is a very normal way to say you enjoy doing something.

After volim, Croatian commonly uses the infinitive to say that you like doing something.

So:

• volim + infinitive

Examples:

• Volim kuhati. = I like cooking / to cook.
• Volim plivati. = I like swimming / to swim.
• Volim sjediti. = I like sitting / to sit.

This is very natural Croatian.

This is a very important verb pair.

• sjediti = to be sitting, to sit in an ongoing state
• sjesti = to sit down once, the action of taking a seat

So:

• Volim sjediti uz rijeku. = I enjoy being seated / sitting by the river.
• Volim sjesti uz rijeku. = I like to sit down by the river.

In your sentence, sjediti fits better because it describes a habitual, ongoing activity, not just the moment of sitting down.

Because the preposition uz normally takes the accusative case, and rijeka changes in the accusative singular.

• nominative: rijeka = river
• accusative: rijeku

So:

• uz rijeku = by / along / next to the river

This is why the ending changes from -a to -u.

Here uz means something like:

• by
• beside
• next to
• sometimes along

So sjediti uz rijeku means sitting by the river or beside the river.

It suggests being close to the river, often right next to it.

Yes. Those are also natural ways to say by the river.

For example:

• Volim sjediti pokraj rijeke.
• Volim sjediti pored rijeke.

These use the genitive case:

• rijeka → rijeke

The sentence with uz rijeku is still completely correct and natural, but pokraj rijeke and pored rijeke may sound slightly more like beside / next to in a purely locational sense.

Navečer is an adverb meaning:

• in the evening
• during the evening
• sometimes toward evening

It is written as one word.

So:

• u večer is not the normal choice here
• navečer is the standard adverb

Examples:

• Radim navečer. = I work in the evening.
• Čitam navečer. = I read in the evening.

In your sentence, it tells you when the action happens.

Croatian word order is fairly flexible. The original sentence is natural, but you can move navečer for emphasis or style.

For example:

• Volim sjediti uz rijeku navečer.
• Navečer volim sjediti uz rijeku.
• Volim navečer sjediti uz rijeku.

These all mean basically the same thing, but the emphasis changes slightly.

The original version sounds neutral and natural.

It normally expresses a general preference or habit, not something happening at this moment.

• Volim sjediti uz rijeku navečer. = I like sitting by the river in the evening.

It means this is something the speaker enjoys in general.

If you wanted to describe what you are doing right now, Croatian would usually use a different structure, for example:

• Sjedim uz rijeku. = I am sitting by the river.

You mainly learn noun gender together with the noun, but the form helps too:

• many nouns ending in -a are feminine
• rijeka is a feminine noun

That is why the accusative singular becomes:

• rijeka → rijeku

This -a → -u pattern is very common for feminine nouns.

Examples:

• knjiga → knjigu
• žena → ženu
• ulica → ulicu

Yes. Both are good English translations.

That is because:

• volim can be I like or I love
• sjediti can be rendered as to sit or sitting
• navečer can be in the evening

So several English versions work:

• I like sitting by the river in the evening.
• I like to sit by the river in the evening.
• I love sitting by the river in the evening.

The Croatian sentence itself is broad enough to allow those slight differences.

A rough pronunciation guide is:

• Volim ≈ VOH-leem
• sjediti ≈ SYEH-dee-tee
• uz ≈ ooz
• rijeku ≈ RYEH-koo
• navečer ≈ nah-VEH-cher

A smoother full reading would sound roughly like:

VOH-leem SYEH-dee-tee ooz RYEH-koo nah-VEH-cher

A few useful notes:

• j in Croatian sounds like English y
• č sounds like ch
• r is rolled or tapped more than in English