Dokumente ću staviti u plavi fascikl i dodati jednu spajalicu.

Because dokumente is the accusative plural, which is used for the direct object of the verb staviti (to put).

• Nominative plural: dokumenti = documents (as the subject)
• Accusative plural: dokumente = documents (as the object)

In this sentence, the speaker is putting the documents somewhere, so documents is the object:

• Dokumente ću staviti... = I will put the documents...

Ću is the 1st person singular future auxiliary, meaning I will.

Croatian often forms the future tense with:

• a form of htjeti (to want, used as an auxiliary in the future)
• • the infinitive

So:

• ću staviti = I will put
• ću dodati = I will add

In this sentence, ću only appears once, but it applies to both verbs:

• Dokumente ću staviti u plavi fascikl i dodati jednu spajalicu.
• literally: The documents I will put into the blue folder and add one paperclip.

This is because ću is a clitic in Croatian. Clitics usually take the second position in the clause.

So instead of:

• Ću dokumente staviti... (not normal here)

Croatian prefers:

• Dokumente ću staviti...

This second-position behavior is very common with short unstressed words like:

• sam, si, je, smo
• ću, ćeš, će
• ga, je, ih
• se

So the placement is grammatical and natural, even though it may feel unusual to an English speaker.

Because Croatian future tense is commonly built with:

• the auxiliary ću
• • the infinitive of the main verb

So:

• ću staviti = I will put
• ću dodati = I will add

The infinitive form here is:

• staviti = to put
• dodati = to add

This is a normal future construction.

Because u can take two different cases, depending on meaning:

• u + accusative = motion into something
• u + locative = location in something

Here the meaning is movement:

• put the documents into the blue folder

So Croatian uses the accusative:

• u plavi fascikl

Compare:

• Dokumenti su u plavom fasciklu. = The documents are in the blue folder.
  (location, so locative)
• Stavit ću dokumente u plavi fascikl. = I will put the documents into the blue folder.
  (movement, so accusative)

Both words are in the accusative singular masculine inanimate:

• fascikl is a masculine noun
• plavi agrees with it in gender, number, and case

For masculine inanimate nouns, the accusative singular usually looks the same as the nominative singular:

• nominative: plavi fascikl
• accusative: plavi fascikl

So although it looks unchanged, it is still accusative because of the preposition u expressing motion.

It is in the accusative singular, because it is the direct object of dodati (to add).

Base forms:

• jedna = one (feminine nominative)
• spajalica = paperclip (feminine nominative)

Accusative singular feminine:

• jednu spajalicu

So:

• dodati jednu spajalicu = to add one paperclip

This is a good example of adjective/number agreement with a feminine noun:

• jedna spajalica (nominative)
• jednu spajalicu (accusative)

Because the speaker specifically says one paperclip.

Croatian, like English, can include the number for precision:

• dodati spajalicu = add a paperclip
• dodati jednu spajalicu = add one paperclip

Using jednu can:

• make the quantity explicit
• add a bit of emphasis
• sound more precise

So both are possible, but jednu spajalicu clearly means one.

Because one auxiliary can govern both infinitives when they share the same subject and tense.

So:

• Dokumente ću staviti u plavi fascikl i dodati jednu spajalicu.

means:

• I will put the documents into the blue folder and add one paperclip.

You could also say:

• Dokumente ću staviti u plavi fascikl i ću dodati jednu spajalicu.

But that is not natural. Croatian normally uses ću only once in this kind of coordinated structure.

Because staviti and dodati are perfective verbs, and perfective verbs are very common when talking about single completed future actions.

Here the speaker means:

• they will put the documents in
• they will add a paperclip
• each action is seen as a complete event

Compare:

• staviti / dodati = perfective, completed action
• stavljati / dodavati = imperfective, repeated/ongoing/habitual action

So this sentence sounds like:

• I’ll put them in and add a paperclip not
• I’ll be putting / keep adding

Yes. Fascikl is masculine.

You can see that from forms like:

• nominative singular: fascikl
• accusative singular: fascikl
• locative singular: u fasciklu

Because it is masculine, the adjective also appears in masculine form:

• plavi fascikl

Yes, Croatian word order is relatively flexible, but not all versions sound equally natural or emphasize the same thing.

The original:

• Dokumente ću staviti u plavi fascikl i dodati jednu spajalicu.

This is natural and gives some focus to dokumente.

You could also hear:

• Stavit ću dokumente u plavi fascikl i dodati jednu spajalicu.

This is also very natural.

What usually stays important is:

• clitics like ću need proper placement
• case endings show grammatical roles, so word order is freer than in English

So the sentence can be rearranged somewhat, but the original is perfectly normal.

In this sentence, spajalica means paperclip.

That is a useful word to remember because English speakers may confuse it with other office items. In Croatian:

• spajalica = paperclip
• klamerica = stapler
• spajalica za papir can also be used if someone wants to be extra clear

So:

• dodati jednu spajalicu = add one paperclip

A very common everyday version would be:

• Stavit ću dokumente u plavi fascikl i dodati jednu spajalicu.

This starts with the verb phrase and may feel a bit closer to English rhythm. But the original version is also correct and natural.

So you can think of:

• Dokumente ću staviti... = slightly fronted documents
• Stavit ću dokumente... = more neutral flow in many contexts