Zalepi kutiju lepljivom trakom.

Zalepi is the imperative form of the verb zalepiti, for one person in an informal command.

• zalepiti = to stick, glue, paste, tape, seal by sticking
• zalepi! = stick it / tape it / seal it!

This verb is also perfective, so it suggests a completed action: not just be taping, but tape it up / get it stuck shut.

For comparison:

• zalepi! = tape it / stick it on
• zalepite! = tape it (to several people, or one person politely)

In Serbian, the subject is often left out because the verb form already shows who is meant.

So in:

• Zalepi kutiju lepljivom trakom.

the form zalepi already tells you this is a command to you (singular, informal).

Serbian does not need to say ti unless the speaker wants emphasis, contrast, or clarity.

For example:

• Ti zalepi kutiju. = You tape the box.
  This sounds more emphatic, like distinguishing one person from another.

Because kutiju is in the accusative case, which is the case used for the direct object.

The noun is:

• kutija = box

In this sentence, the box is the thing being taped, so it becomes the direct object:

• zalepi kutiju = tape the box

This is a feminine noun ending in -a, and many such nouns change like this:

• nominative: kutija
• accusative: kutiju

So the ending -u is not random; it marks the object of the action.

Because Serbian uses the instrumental case to show the means or tool used to do something.

Here, lepljivom trakom means with adhesive tape / using adhesive tape.

The base phrase is:

• lepljiva traka = adhesive tape

In the instrumental singular, it becomes:

• lepljivom trakom

So the pattern is:

• zalepi kutiju lepljivom trakom = tape the box with adhesive tape

This is very common in Serbian. The instrumental often answers the question with what?

Examples:

• Pišem olovkom. = I write with a pencil.
• Sečem nožem. = I cut with a knife.

The dictionary forms are:

• zalepiti = to stick, tape, glue, seal by sticking
• kutija = box
• lepljiv = sticky / adhesive
• traka = strip, tape, band

In the sentence, some words change form because of grammar:

• zalepi ← from zalepiti
• kutiju ← from kutija
• lepljivom ← from lepljiv
• trakom ← from traka

Yes, lepljiva traka is a normal and clear way to say adhesive tape.

Depending on context, Serbian speakers may also use other expressions, such as:

• selotejp = Scotch tape / sticky tape / clear tape
• traka = tape, if the context is already clear

So:

• Zalepi kutiju lepljivom trakom. sounds natural and somewhat neutral.
• Zalepi kutiju selotejpom. also sounds very natural in everyday speech if you mean that specific kind of tape.

This is mainly a question of aspect, which is very important in Serbian.

• lepiti = imperfective
• zalepiti = perfective

Very roughly:

• lepiti focuses on the process, repetition, or ongoing action
• zalepiti focuses on completing the action

So:

• Lepi kutiju. can sound like be taping the box / tape the box with more focus on the activity
• Zalepi kutiju. sounds more like tape up the box / get it sealed

In commands, Serbian often prefers the perfective when the goal is a completed result.

Yes. Serbian word order is fairly flexible, because cases show the grammatical roles.

The neutral order here is:

• Zalepi kutiju lepljivom trakom.

But you could also hear:

• Kutiju zalepi lepljivom trakom.
• Lepljivom trakom zalepi kutiju.

These versions change the focus or emphasis, not the basic meaning.

For example:

• Lepljivom trakom zalepi kutiju. emphasizes the method: Use adhesive tape to tape the box.

So English relies heavily on word order, while Serbian can move words around more freely because endings carry much of the grammar.

It can mean several related things: stick, glue, paste, tape, or seal by sticking something on. The exact English translation depends on the object and the material used.

In this sentence, because of lepljivom trakom, the best interpretation is clearly tape the box or seal the box with adhesive tape.

So the verb itself is a bit broader than any one English verb, and the rest of the sentence helps narrow it down.

You would use zalepite instead of zalepi.

• Zalepi kutiju lepljivom trakom. = singular informal
• Zalepite kutiju lepljivom trakom. = plural, or singular polite/formal

This is like the common Serbian distinction between:

• ti forms = singular informal
• vi forms = plural or polite

So if you are speaking to a stranger, a customer, a teacher, or any situation requiring politeness, zalepite is the safer choice.