Elli kişi geldi.

After numbers in Turkish, the noun usually stays in the singular.

• elli kişi = fifty people
• üç kitap = three books
• on öğrenci = ten students

So kişiler would normally not be used after elli.
This is different from English, where we say fifty people with a plural noun.

In Turkish, when the subject is a number expression like elli kişi, the verb is very often kept in 3rd person singular.

• Elli kişi geldi. = natural, standard
• Elli kişi geldiler. = generally not preferred in standard Turkish

So even though the meaning is plural, Turkish commonly uses a singular verb with counted groups.

Kişi means person and is especially common in counting and more neutral/formal contexts.

• elli kişi = fifty people
• iki kişi = two people

İnsan also means human / person / people, but it is not normally the best choice after a number in this kind of sentence.

So:

• elli kişi = natural
• elli insan = possible in some contexts, but less standard for simple counting

Geldi is the simple past (also called the definite past) of gelmek = to come.

Breakdown:

• gel- = come
• -di = past tense marker

So:

• geldi = he/she/it came or they came, depending on context

In this sentence, it means came with the subject elli kişi.

Turkish normally puts the finite verb at the end of the sentence.

So:

• Elli kişi geldi. is the neutral, standard order.

This is one of the most important word-order patterns in Turkish.
English usually says Fifty people came, with the verb in the middle, but Turkish prefers subject + verb at the end.

Yes, but changing the order usually changes the focus or emphasis.

The most neutral version is:

• Elli kişi geldi.

You may also hear:

• Geldi elli kişi.

That second version is more marked and can sound like It was fifty people who came or can fit a special context in speech or storytelling. For a learner, Elli kişi geldi is the safest standard pattern.

By itself, elli kişi normally means exactly fifty people.

If you want to say about fifty people, Turkish usually adds another word, for example:

• yaklaşık elli kişi = about fifty people
• elli kadar kişi = around fifty people

So without anything extra, the default reading is exactly fifty.

Turkish does not use articles the same way English does.

• There is no direct word that works exactly like English the in every case.
• Bir can sometimes mean a/an, but it is not used in number expressions like this one.

So Elli kişi geldi is perfectly complete without any article.

Depending on context, English might translate it as:

• Fifty people came
• The fifty people came only if the context specifically makes them definite, but Turkish does not mark that here in the same way.

A few useful points:

• ş is pronounced like sh
• i is the regular dotted i sound
• kişi sounds roughly like kee-SHEE

And for the whole sentence:

• elli ≈ EL-lee
• kişi ≈ kee-SHEE
• geldi ≈ GEL-dee

So the whole sentence is roughly:

• EL-lee kee-SHEE GEL-dee

Normally, no. After a number, Turkish uses the singular noun:

• elli kişi ✔
• elli kişiler ✘

This is one of the most common mistakes for English speakers, because English uses plural nouns after numbers, but Turkish usually does not.

Yes. Kişi refers to a person / human being. It is not used for animals or objects.

So:

• elli kişi = fifty people
• not for fifty books, fifty cats, etc.

For other nouns, Turkish still keeps the noun singular after numbers:

• elli kitap = fifty books
• elli kedi = fifty cats

So the grammar pattern is broad, but kişi itself is specifically human.