Mahkeme ona hapis cezası verdi.

A useful breakdown is:

• Mahkeme = the court
  This is the subject.
• ona = to him / her
  This is the indirect object.
• hapis cezası = a prison sentence
  This is the direct object.
• verdi = gave
  This is the verb, in the simple past.

So the structure is basically:

Subject + Indirect Object + Direct Object + Verb

which is a very common Turkish word order.

Because ona is the dative form of o.

• o = he / she / it
• ona = to him / to her / to it

In this sentence, the court gives the sentence to someone, so Turkish uses the dative.

With o, the dative form is irregular-looking because of the extra n:

• o → ona
• bu → buna
• şu → şuna

That n is a buffer consonant.

It can mean either one.

Turkish third-person pronouns do not mark gender:

• o = he / she / it
• ona = to him / to her / to it

So you only know whether it is him or her from context.

Hapis cezası is the normal Turkish expression for prison sentence.

Literally:

• hapis = imprisonment / prison
• ceza = punishment / penalty
• cezası = its punishment / penalty in a compound form

So the whole phrase means something like:

the penalty of imprisonment → a prison sentence

This is a very common legal expression.

Because hapis cezası is a noun compound.

In Turkish, when one noun modifies another noun in this kind of compound, the second noun usually takes a special ending, often called the third-person possessive ending:

• ceza → cezası
• kapı → kapısı
• durağ → durağı

So:

• hapis cezası = prison sentence
• ölüm cezası = death penalty
• trafik cezası = traffic fine

Even though it looks possessive in English grammar terms, in Turkish this is just the normal way many noun compounds are formed.

Because the direct object here is non-specific / indefinite.

In Turkish, a direct object often behaves like this:

• bare form = a nonspecific object
• accusative form = a specific, definite object

So:

• hapis cezası verdi = gave/imposed a prison sentence
• hapis cezasını verdi = gave/imposed the prison sentence or that particular prison sentence

In your sentence, the meaning is more general: the court sentenced him/her to prison, not necessarily referring to one already identified sentence.

Because Turkish commonly uses vermek (to give) with punishments, sentences, and penalties.

So Turkish says things like:

• ceza vermek = to give a punishment / punish
• hapis cezası vermek = to give a prison sentence
• para cezası vermek = to give a fine

In English, legal language can also use give:

• The court gave him a prison sentence.

So this usage is quite natural in both languages.

Verdi is the simple past tense of vermek (to give).

• vermek = to give
• verdi = gave

This tense is often called the -DI past in Turkish. It is the normal past tense used for a completed action.

So Mahkeme ona hapis cezası verdi means the action is completed:
the court gave / imposed the sentence.

No, Turkish word order is flexible, although Subject + Indirect Object + Direct Object + Verb is very natural here.

Your sentence:

• Mahkeme ona hapis cezası verdi.

Other possible orders are:

• Ona mahkeme hapis cezası verdi.
• Mahkeme hapis cezasını ona verdi.

These are not all exactly identical in emphasis. Turkish changes word order to change focus, topic, or emphasis.

But for a learner, the original sentence is a very standard and safe order.

Because Turkish does not have articles exactly like English a/an/the.

Sometimes bir can mean a/an, but it is not always necessary.

So:

• hapis cezası verdi can naturally mean gave a prison sentence
• bir hapis cezası verdi would be possible in some contexts, but it is less neutral here

Turkish usually shows definiteness in other ways, especially through:

• context
• word order
• the accusative ending on direct objects

That is why English needs a prison sentence, but Turkish can simply say hapis cezası.

It can mean court in a general sense, but in this sentence it means the legal body / judicial authority, not the building.

So here mahkeme is functioning like:

• the court
• the judge/court system acting officially

In other words, it is the entity that gives the sentence.

Yes. Turkish has several ways to express the same idea. For example:

• Mahkeme onu hapse mahkûm etti.
  = The court sentenced him/her to prison.

• Mahkeme ona hapis cezası verdi.
  = The court gave him/her a prison sentence.

Your sentence is perfectly natural and very common, especially in formal or news-style language.