Η διανομή ρόλων δείχνει πρωταγωνιστικό ρόλο και δευτερεύοντα ρόλο.

Because διανομή ρόλων means distribution of roles or casting. In Greek, a noun is often followed by another noun in the genitive to show a relationship like of in English.

• η διανομή = the distribution
• ρόλων = of roles

So η διανομή ρόλων literally means the distribution of roles.

Both are possible, but they mean slightly different things.

• η διανομή ρόλων = role distribution / casting in a general sense
• η διανομή των ρόλων = the distribution of the roles, referring to specific roles already known in context

So the version without the article is more general and more compact.

Η διανομή is in the nominative singular and it is the subject of the sentence.

• η = the feminine singular nominative article
• διανομή = a feminine noun

It is the thing that does the action of δείχνει.

δείχνει is the 3rd person singular present tense of δείχνω, meaning to show.

So:

• δείχνω = I show
• δείχνει = he/she/it shows

Here it agrees with η διανομή, which is singular, so δείχνει means shows.

Because they are the direct objects of δείχνει.

The verb δείχνει answers the question shows what?

It shows:

• πρωταγωνιστικό ρόλο
• δευτερεύοντα ρόλο

That is why those noun phrases are in the accusative singular.

Because they belong to different adjective patterns in Greek.

• πρωταγωνιστικός follows the regular -ικός adjective pattern
  
  • accusative masculine singular: πρωταγωνιστικό
• δευτερεύων follows a different pattern, based on an older participle-type adjective
  
  • accusative masculine singular: δευτερεύοντα

Both agree with ρόλο, which is masculine singular accusative, but they reach that form through different declension patterns.

Because the sentence is presenting the roles in a more general or categorizing way, not pointing to two specific already-identified roles.

So this sounds like:

• a leading role and a supporting role

If you wanted to make them explicitly indefinite, you could also say:

• έναν πρωταγωνιστικό ρόλο και έναν δευτερεύοντα ρόλο

And if they were specific, you could use definite articles:

• τον πρωταγωνιστικό ρόλο και τον δευτερεύοντα ρόλο

It is a very natural expression. Depending on context, διανομή ρόλων can mean:

• casting
• assignment of roles
• distribution of roles

In theater, film, or TV contexts, it often corresponds to casting.

It is repeated because the sentence refers to two separate kinds of role.

• πρωταγωνιστικό ρόλο
• δευτερεύοντα ρόλο

Greek could sometimes avoid repetition in other contexts, but here the repetition is clear and natural. It helps show that these are two distinct categories, not two adjectives describing one single role.

It means leading role or starring role.

It comes from πρωταγωνιστικός, related to πρωταγωνιστής, meaning protagonist or leading actor/performer.

So πρωταγωνιστικός ρόλος is the role with primary importance.

It means secondary role or supporting role.

The adjective δευτερεύων means secondary or of lesser importance compared with the main one.

So δευτερεύων ρόλος is a role that is not the main one.

No, Greek word order is more flexible than English word order, although this sentence uses a very normal and straightforward order:

• subject: Η διανομή ρόλων
• verb: δείχνει
• objects: πρωταγωνιστικό ρόλο και δευτερεύοντα ρόλο

This is the most neutral way to say it. Greek could rearrange parts for emphasis, but this version is standard and easy to understand.