Punjač je u kancelariji; zaboravila si ga juče na stolu.

This is the past tense in Serbian.

It is made with:

• the l-participle: zaboravila
• the auxiliary verb biti in the present: si

So zaboravila si = you forgot

Why this order? In Serbian, short unstressed words like si usually go in the second position of the clause. That is why zaboravila si ga sounds natural here.

Also, zaboravila shows that the person being addressed is female.
If you were speaking to a man, it would be:

• zaboravio si ga

You can sometimes hear different word orders in speech, but zaboravila si is the standard natural pattern here.

Because it agrees with the gender of the person being addressed.

In Serbian past tense, the participle changes for gender:

• zaboravio = a man forgot
• zaboravila = a woman forgot
• zaboravilo = it forgot

So zaboravila si means you (female) forgot.

This is very different from English, where the verb does not change depending on whether the person is male or female.

Because Serbian often drops subject pronouns when they are already clear from the verb form.

In:

• zaboravila si

the si already tells us this is you singular, and zaboravila tells us the person addressed is female.

So ti is unnecessary unless you want emphasis or contrast:

• Ti si ga zaboravila = You are the one who forgot it

Without emphasis, Serbian usually leaves ti out.

Ga means him/it, but in this sentence it means it, referring to punjač.

Punjač is a masculine noun, so when it becomes a direct object, the short pronoun is:

• ga = him/it (accusative singular masculine animate/inanimate in the short clitic form for masculine/neuter pronouns; in practice here it is the normal short object pronoun for punjač)

So:

• zaboravila si ga = you forgot it

If the object were feminine, the pronoun would be different:

• knjiga → zaboravila si je = you forgot it (the book)

Because this sentence describes location, not movement.

• u kancelariji = in the office → where something is
• u kancelariju = into the office → where something is going

After u:

• locative is used for being somewhere
• accusative is used for motion toward somewhere

Here the charger is already there:

• Punjač je u kancelariji. = The charger is in the office.

So kancelariji is the locative singular form of kancelarija.

For the same reason as u kancelariji: this is location, not direction.

• na stolu = on the table / at the table → location
• na sto = onto the table → movement toward the surface

Since the meaning is that the charger was left there, the table is just the place where it stayed, so Serbian uses the locative:

• na stolu

Stolu is the locative singular of sto (table).

The basic form is:

• sto

But after na when it means on in the sense of location, Serbian uses the locative:

• na stolu

So the noun changes form because Serbian marks grammatical function with cases.

Je is the 3rd person singular present form of biti (to be).

So:

• Punjač je u kancelariji = The charger is in the office

It functions just like is in English.

Compare:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

Yes, juče can move around.

In the sentence:

• zaboravila si ga juče na stolu

juče means yesterday and is an adverb of time.

Serbian word order is relatively flexible, so you could also say:

• Juče si ga zaboravila na stolu.
• Zaboravila si ga na stolu juče.

These all mean basically the same thing, but the emphasis changes a little:

• Juče at the beginning highlights when
• na stolu later highlights where
• the original sentence sounds natural and neutral

The semicolon links two closely related statements:

• Punjač je u kancelariji
• zaboravila si ga juče na stolu

The second part explains the first:

• The charger is in the office;
• you forgot it on the table yesterday.

In everyday writing, many people might also use:

• a period
• a comma
• or even jer / pošto style restructuring

For example:

• Punjač je u kancelariji. Zaboravila si ga juče na stolu.

That is also perfectly natural.

No. Kancelarija is a very common word for office, especially in many standard and everyday contexts.

Depending on region and style, you may also see:

• ured

Both can mean office, but usage can vary by country/region within the Serbian/Croatian/Bosnian/Montenegrin area.

In this sentence, kancelarija is completely normal and natural Serbian.

Yes, Serbian allows quite a lot of word-order flexibility, though not every version sounds equally natural.

For example:

• Punjač je u kancelariji; juče si ga zaboravila na stolu.
• Juče si ga zaboravila na stolu; punjač je u kancelariji.
• U kancelariji je punjač; zaboravila si ga juče na stolu.

The meaning stays close, but the emphasis changes.

Still, some things are less flexible:

• the clitic si tends to stay near the beginning of its clause
• the short pronoun ga also follows clitic-placement rules

So although Serbian word order is flexible, it is not random.

Because Serbian and English divide this idea differently.

English often says:

• You left it on the table

But Serbian can naturally say:

• Zaboravila si ga na stolu literally, You forgot it on the table

This means that you forgot it there, i.e. you left it there by mistake.

So Serbian uses zaboraviti in a way that often matches English forget, but in this kind of context it can also express the idea of accidentally leaving something somewhere.