Ο προπονητής λέει ότι η νίκη είναι πολύ σημαντική σήμερα.

Greek articles change for gender, number, and case.

• ο = the for a masculine singular noun in the nominative case
• η = the for a feminine singular noun in the nominative case

So:

• ο προπονητής = the coach
• η νίκη = the victory

Unlike English, Greek does not use one single word for the in all situations.

Because προπονητής is a masculine noun in Greek. Nouns have grammatical gender, and you simply learn each noun together with its article:

• ο προπονητής = the coach

A good habit is to memorize new Greek nouns with their article, not by themselves. That helps you remember the noun’s gender and use adjectives correctly later.

Λέει is the 3rd person singular present form of λέω, which means to say or to tell.

So ο προπονητής λέει means:

• the coach says
• or, depending on context, the coach is saying

Greek present tense often covers both the simple present and the present progressive that English separates.

Ότι means that and introduces a subordinate clause.

So:

• Ο προπονητής λέει ότι... = The coach says that...

In English, that is often optional:

• The coach says victory is very important today

In Greek, using ότι is very normal and clear here.

You may also see πως used in a similar way in everyday Greek:

• λέει ότι...
• λέει πως...

Both can mean says that...

Greek often uses the definite article more regularly than English.

• η νίκη = the victory

In this sentence, the speaker is talking about the victory as a specific idea or result that matters in the situation. Greek commonly includes the article in places where English might sound more natural without it or where article use feels different.

So even if English might sometimes say victory is important today, Greek naturally says η νίκη είναι...

Because adjectives in Greek must agree with the noun they describe.

Here, the noun is:

• η νίκη = feminine singular

So the adjective must also be feminine singular:

• σημαντική = important

You can see the agreement in:

• η νίκη είναι πολύ σημαντική

If the noun were masculine or neuter, the adjective form would change:

• ο αγώνας είναι σημαντικός = the match is important
• το αποτέλεσμα είναι σημαντικό = the result is important

Πολύ here means very.

It is modifying the adjective σημαντική:

• πολύ σημαντική = very important

In this use, πολύ is an adverb, so it does not change for gender or number.

Be careful: πολύς / πολλή / πολύ can also function as an adjective meaning much / many, and then it does change. But in this sentence, it is simply the adverb very.

Greek word order is more flexible than English word order. Putting σήμερα at the end is completely natural.

• Ο προπονητής λέει ότι η νίκη είναι πολύ σημαντική σήμερα.

This is a neutral, natural order meaning today applies to the statement about importance.

Greek can move adverbs around for emphasis, but the basic meaning stays similar. For example:

• Σήμερα η νίκη είναι πολύ σημαντική.
• Η νίκη είναι σήμερα πολύ σημαντική.

All are possible, though some may sound more marked depending on context.

In this sentence, the most natural reading is:

• today, victory is very important
• or the victory is very important today

So σήμερα most naturally modifies the idea of being important, not necessarily the timing of the victory itself.

In real conversation, context decides the exact nuance. But grammatically, the sentence most naturally emphasizes the importance today.

Greek does not have a separate tense exactly like the English continuous in the same way.

• λέει can mean says or is saying
• είναι means is

The present tense in Greek often covers both:

• simple present
• present continuous

So context tells you whether to translate more naturally as says or is saying.

A rough pronunciation guide is:

• Ο προπονητής = o pro-po-ni-TIS
• λέει = LE-i
• ότι = O-ti
• η νίκη = i NI-ki
• είναι = I-ne
• πολύ = po-LI
• σημαντική = si-man-di-KI
• σήμερα = SI-me-ra

A few useful pronunciation notes:

• η, ι, ει, οι, υ often sound like ee in modern Greek
• the written accent mark shows which syllable is stressed
• ντ in σημαντική is pronounced like d

So the whole sentence sounds approximately like:

• o pro-po-ni-TIS LE-i O-ti i NI-ki I-ne po-LI si-man-di-KI SI-me-ra

Yes, Greek often drops subject pronouns and sometimes even leaves the subject understood from context, because the verb ending already gives information.

• λέει ότι... = he/she says that...

But in your sentence, ο προπονητής is included to make it clear who is speaking:

• Ο προπονητής λέει ότι... = The coach says that...

So including the noun makes the sentence explicit and natural.