Ο νικητής χαμογελάει.

A good English-style approximation is:

o nee-kee-TEES ha-mo-ye-LA-ee

A few sound notes:

• Ο = o as in for (short, clean o sound)
• νικητής = nee-kee-TEES
• χ in χαμογελάει is not exactly English h; it is a harsher sound, like ch in German Bach
• γ before ε sounds like a y sound, so γε sounds roughly like ye
• The stress falls on:
  • νικητής → last syllable
  • χαμογελάει → λά

Because it is the first word of the sentence.

Normally, the article is written ο with a lowercase letter. At the beginning of a sentence, it becomes Ο, just like English the becomes The at the start of a sentence.

So:

• Ο νικητής χαμογελάει. = at the beginning of a sentence
• Βλέπω τον νικητή. = not at the beginning

ο means the.

More specifically, it is the masculine singular nominative definite article. Greek articles change according to:

• gender
• number
• case

Here it is ο because νικητής is:

• masculine
• singular
• the subject of the sentence

So ο νικητής = the winner.

νικητής is a noun meaning winner.

In this sentence, it is:

• masculine
• singular
• nominative case

The nominative is the form usually used for the subject of the sentence, and here the winner is the one doing the action of smiling.

You may also notice that νικητής ends in -ής, which is a common ending for some masculine nouns in Greek.

Usually, yes: νικητής is the masculine form.

If the winner is female, Greek normally uses νικήτρια.

So:

• Ο νικητής χαμογελάει. = The male winner is smiling / smiles.
• Η νικήτρια χαμογελάει. = The female winner is smiling / smiles.

As in many languages, the masculine form can sometimes be used more generally in some contexts, but if you know the winner is female, the normal form is νικήτρια.

χαμογελάει is the verb, and it is:

• present tense
• 3rd person singular
• from the verb χαμογελώ or χαμογελάω = to smile

So χαμογελάει means:

• he smiles
• she smiles
• it smiles
• or, depending on context, is smiling

In Greek, the present tense often covers both the English simple present and present progressive:

• Ο νικητής χαμογελάει.
  • The winner smiles.
  • The winner is smiling.

Both are possible depending on context.

Because Greek often leaves subject pronouns out when they are not needed.

This is possible because the verb ending already tells you the person and number. In χαμογελάει, the ending shows 3rd person singular.

So Greek does not need to say he or she unless there is a special reason to emphasize it or avoid confusion.

In this sentence, the subject is already stated as ο νικητής, so adding a pronoun would be unnecessary.

The accent marks show which syllable is stressed.

In Modern Greek, stress is very important, and it is written clearly.

Here:

• νικητής → stress on -τής
• χαμογελάει → stress on -λά-

This helps you pronounce the words correctly. Greek stress is not optional: putting the stress in the wrong place can sound unnatural, and sometimes it can even change meaning in other words.

Yes. χαμογελά is also a common and correct form.

For this verb, both forms are used in Modern Greek:

• χαμογελάει
• χαμογελά

So both of these are acceptable:

• Ο νικητής χαμογελάει.
• Ο νικητής χαμογελά.

A learner should recognize both. The meaning is the same.

Yes. Greek word order is more flexible than English.

The most neutral order here is:

• Ο νικητής χαμογελάει.

But you can also say:

• Χαμογελάει ο νικητής.

That can sound more like you are focusing on the action or fitting the sentence into a particular context.

So the basic meaning stays the same, but the emphasis can shift slightly depending on word order.