Lekar je prepisao dve tablete.

Je is the auxiliary verb used to form the perfect tense in Serbian.

So je prepisao means something like has prescribed / prescribed.

A useful breakdown is:

• lekar = doctor
• je = auxiliary for past tense
• prepisao = prescribed

In English, je may look like is, but here it does not mean is. It is part of the past-tense verb form.

In Serbian, many past-tense forms are made with:

• a form of biti (to be) as an auxiliary
• plus a past participle

So:

• je = auxiliary
• prepisao = past participle

Together they form the past tense.

This is very common in Serbian:

• On je došao. = He came / He has come.
• Lekar je prepisao... = The doctor prescribed...

Because prepisao agrees with the subject in gender and number.

Here the subject is lekar, which is masculine singular, so the participle is also masculine singular:

• prepisao = masculine singular
• prepisala = feminine singular
• prepisalo = neuter singular
• prepisali = plural masculine/mixed
• prepisale = plural feminine

Examples:

• Lekar je prepisao dve tablete.
• Lekarka je prepisala dve tablete.

So the ending tells you something about who did the action.

Because tableta is a feminine noun.

In Serbian, 2 has different forms depending on gender:

• dva for masculine and neuter nouns
• dve for feminine nouns

Examples:

• dva dana = two days
• dva sela = two villages
• dve tablete = two tablets

Since tableta is feminine, dve is the correct form.

After dva/dve, tri, and četiri, the noun usually appears in a form that matches the genitive singular for many nouns.

So:

• jedna tableta
• dve tablete
• tri tablete
• četiri tablete

But:

• pet tableta
• šest tableta

For feminine nouns ending in -a, this often means:

• nominative singular: tableta
• genitive singular: tablete
• genitive plural: tableta

That is why you get:

• dve tablete but
• pet tableta

This number pattern is something learners usually need to memorize.

Lekar is in the nominative singular because it is the subject of the sentence.

It answers the question Who prescribed two tablets?

• lekar = the doctor

If Serbian changes the role of the noun, the form may change too, but here it stays in the basic dictionary form because it is the subject.

Because Serbian does not have articles like English a/an and the.

So lekar can mean:

• a doctor
• the doctor

The exact meaning depends on context.

Likewise, tablete can mean tablets without an article.

Serbian relies on context, word order, and sometimes stress or additional words to show definiteness.

The sentence you have is the most neutral and natural order:

• Lekar je prepisao dve tablete.

But Serbian word order is fairly flexible, especially for emphasis. For example:

• Dve tablete je lekar prepisao.
  This puts more focus on two tablets.
• Lekar dve tablete je prepisao.
  Possible in some contexts, but less neutral.
• Prepisao je dve tablete.
  Possible if the subject is already understood.

One important rule: je is a clitic, so it usually appears in second position in the clause.

That is why je comes early in the sentence.

Yes, often you can.

Both lekar and doktor can mean doctor in everyday use.

A rough difference:

• lekar = the standard word for a medical doctor/physician
• doktor = very common in speech, but can also mean someone with a doctorate

So in a medical context, both are often understood as doctor, but lekar is a very straightforward choice here.

They often leave out pronouns, but not usually a full noun like lekar unless the subject is already very clear.

So Serbian commonly drops on/ona:

• Prepisao je dve tablete. = He prescribed two tablets.

This is natural if everyone already knows who he is.

But if you want to explicitly say the doctor, then:

• Lekar je prepisao dve tablete.

is the normal full sentence.

No. Prepisati can have more than one meaning depending on context.

Common meanings include:

• to prescribe
• to copy out / transcribe

In this sentence, because of lekar and tablete, it clearly means to prescribe.

So context tells you which meaning is intended.