Το τέλος της συναυλίας ήταν ήσυχο, γιατί όλοι άκουγαν τη φωνή της τραγουδίστριας.

Το τέλος means the end.

• τέλος is a neuter noun in Greek.
• The definite article for neuter singular in the nominative case is το.

So:

• το τέλος = the end (subject of the sentence)
• Gender: neuter
• Number: singular
• Case: nominative (because it’s the subject of ήταν = was)

της συναυλίας literally means of the concert.

• συναυλία = concert (feminine noun, nominative singular)
• της συναυλίας = of the concert (feminine, genitive singular)

In Greek, possession or “of” relationships are usually shown with the genitive case, not with a separate word like of.

So:

• το τέλος της συναυλίας = the end of the concert
  
  • τέλος = end (neuter, nominative)
  • της συναυλίας = of the concert (feminine, genitive)

Adjectives in Greek must agree with the noun in:

• gender
• number
• case

Here:

• Noun: το τέλος
  
  • neuter, singular, nominative
• Adjective: ήσυχος, -η, -ο (= quiet)

The correct form for neuter, singular, nominative is ήσυχο.

So:

• ήσυχος → masculine
• ήσυχη → feminine
• ήσυχο → neuter

Because τέλος is neuter, you must say:

• το ήσυχο τέλος
• Το τέλος … ήταν ήσυχο.

ήσυχος / ήσυχη / ήσυχο usually means:

• quiet (not noisy)
• or peaceful/calm (no disturbance)

In this sentence:

• Το τέλος της συναυλίας ήταν ήσυχο =
  The end of the concert was quiet / peaceful.

Both quiet and calm work in English, but here the focus is on lack of noise because everyone was listening.

γιατί can mean both:

• why (in questions)
• because (in answers / explanations)

Here it means because:

• … ήταν ήσυχο, γιατί όλοι άκουγαν …
  = … was quiet, because everyone was listening …

You could also use επειδή here with almost the same meaning:

• ήταν ήσυχο, επειδή όλοι άκουγαν …

In everyday speech γιατί is more common and a bit more casual; επειδή can sound slightly more formal or explicit as “since/because”, but both are correct.

Greek uses different past tenses to show aspect (how the action is viewed):

• άκουγαν = imperfect (they were listening / they used to listen)
  
  • describes an ongoing or continuous past action
• άκουσαν = aorist (they listened / they heard)
  
  • describes a completed event as a whole

In this sentence:

• όλοι άκουγαν τη φωνή της τραγουδίστριας
  = everyone was listening to the singer’s voice

The idea is that during the end of the concert, people were in the process of listening, which explains why it was quiet. So the imperfect άκουγαν fits better than the aorist άκουσαν.

όλοι means everyone / all (people).

• It’s the subject of the verb.
• It is masculine plural (used by default for mixed or unknown groups of people).

Because the subject is plural, the verb must also be plural:

• όλοι άκουγαν = everyone was listening / they all were listening

If you added a noun, it might look like:

• Όλοι οι θεατές άκουγαν… = All the spectators were listening…

Greek articles change form depending on case.

• η φωνή = the voice (feminine, nominative singular – subject form)
• τη φωνή = the voice (feminine, accusative singular – direct object form)

Here, τη φωνή is the direct object of the verb άκουγαν:

• όλοι άκουγαν τη φωνή …
  = everyone was listening to the voice …

So it must be in the accusative, hence τη, not η.

τραγουδίστρια means female singer (feminine noun).

Forms:

• η τραγουδίστρια = the singer (nominative)
• της τραγουδίστριας = of the singer (genitive)

The -ας ending here marks the feminine genitive singular.

In the phrase:

• τη φωνή της τραγουδίστριας

you literally have:

• τη φωνή = the voice (object, accusative)
• της τραγουδίστριας = of the singer (possessor, genitive)

Together: the singer’s voice / the voice of the singer.

Both are grammatical, but they express the idea differently:

1. Το τέλος της συναυλίας ήταν ήσυχο

   • Focuses on the end as a “thing/state”:
     The end of the concert was quiet.

2. Η συναυλία τελείωσε ήσυχα

   • Focuses on the action of ending:
     The concert ended quietly.

In the original sentence, using το τέλος as a noun allows you to describe that specific moment/situation (the end) and comment on its quality (ήσυχο) more like a characteristic of that phase.