Uvijek ostavljam ključeve u ladici u hodniku.

Croatian often drops subject pronouns because the verb ending already shows the person.

• ostavljam = I leave / I am leaving

If you added ja, it would sound more emphatic:

• Ja uvijek ostavljam ključeve u ladici u hodniku.

That would mean something like I always leave the keys in the drawer in the hallway.

Ostavljam is the 1st person singular present tense of the verb ostavljati.

• ostavljati = to leave
• ostavljam = I leave / I am leaving

In this sentence, it describes a repeated habit, so the most natural English sense is I always leave.

This is about aspect, which is very important in Croatian.

• ostavljati / ostavljam = imperfective → repeated, ongoing, habitual
• ostaviti / ostavim = perfective → completed action

Because uvijek means always, Croatian normally uses the imperfective form:

• Uvijek ostavljam...

That matches the idea of something you do regularly.

Because ključeve is the accusative plural, and here keys are the direct object of the verb.

Basic forms:

• ključ = key
• ključevi = keys (nominative plural)
• ključeve = keys (accusative plural)

Compare:

• Ključevi su na stolu. = The keys are on the table.
• Ostavljam ključeve u ladici. = I leave the keys in the drawer.

Because after u meaning in, Croatian uses the locative case when talking about location.

So:

• u ladici = in the drawer
• u hodniku = in the hallway

The basic dictionary forms are:

• ladica = drawer
• hodnik = hallway / corridor

In the sentence, they become:

• ladici = locative singular
• hodniku = locative singular

This is the common contrast between location and movement.

• u ladici = in the drawer → location
• u ladicu = into the drawer → movement

In your sentence, the keys are being left there as their location, so u ladici is the right form.

The same idea applies to hodnik:

• u hodniku = in the hallway
• u hodnik = into the hallway

Because Croatian keeps both prepositional phrases:

• u ladici = in the drawer
• u hodniku = in the hallway

The second phrase describes which drawer:

• the drawer in the hallway

So the structure is:

• [u ladici] [u hodniku]
• literally: in the drawer in the hallway

Croatian normally does not drop the second u here.

Croatian often distinguishes between:

• u = in, inside
• na = on, at, onto, depending on context

A drawer is an enclosed space, so:

• u ladici = in the drawer

A hallway is also treated as a space you are inside, so:

• u hodniku = in the hallway

Compare:

• na stolu = on the table
• u ladici = in the drawer

No. Croatian word order is fairly flexible because case endings show what each word is doing.

The given sentence is a very natural, neutral order:

• Uvijek ostavljam ključeve u ladici u hodniku.

But you could also say:

• Ključeve uvijek ostavljam u ladici u hodniku.
• U ladici u hodniku uvijek ostavljam ključeve.

The meaning stays basically the same, but the emphasis changes.

Yes. Uvijek is quite flexible.

Common possibilities include:

• Uvijek ostavljam ključeve...
• Ključeve uvijek ostavljam...

Putting uvijek near the beginning is very common and sounds natural in everyday Croatian.

Because Croatian has no articles like English a / an / the.

So Croatian simply says:

• ključeve
• ladici
• hodniku

Whether English would use a or the is understood from context.

In this sentence, because of uvijek, it is understood as a habit:

• I always leave the keys...

Croatian present tense can sometimes match either English simple present or present continuous, but context decides. Here the habitual meaning is clearly the intended one.

A rough English-style guide is KLYOO-cheh-veh.

A few useful points:

• lj is a soft l sound
• č sounds like ch in church
• e is a clear short vowel, not like silent e in English

It does not match English sounds perfectly, but KLYOO-cheh-veh is a helpful approximation for learners.