Η οπαδός στην κερκίδα μιλάει πολύ δυνατά.

Because οπαδός can be used for either a male or a female person, and the noun itself stays the same. The article shows the gender:

• ο οπαδός = the male fan/supporter
• η οπαδός = the female fan/supporter

So in this sentence, η tells you that the fan is female.

στην is the very common contraction of:

• σε = in, at, to
• την = the (feminine accusative singular)

So:

• σε την → στην

Here στην κερκίδα means in the stands, in the bleachers, or at the stand, depending on the context.

After the preposition σε, Modern Greek normally uses the accusative case.

The noun is:

• nominative: η κερκίδα
• accusative: την κερκίδα

In this noun, the word κερκίδα itself looks the same in nominative and accusative singular. The thing that changes is the article:

• η → nominative
• την → accusative

And since σε + την becomes στην, you see στην κερκίδα.

κερκίδα usually refers to the stands, bleachers, or grandstand in a stadium or sports venue.

A useful thing to notice is that Greek may use the singular where English often prefers a plural expression. So στην κερκίδα can naturally be translated as in the stands.

μιλάει is the 3rd person singular present tense of μιλάω / μιλώ.

So it means:

• he/she speaks
• he/she is speaking

Greek present tense can cover both the simple present and the progressive idea, depending on context.

You may also see the shorter form:

• μιλά

Both μιλάει and μιλά are standard.

Because δυνατά is being used as an adverb, not as an adjective.

Here it modifies the verb μιλάει, so it means loudly:

• μιλάει δυνατά = she speaks loudly

If you used an adjective such as δυνατή, that would describe a noun, not the way she speaks.

A helpful pattern is:

• adjective: δυνατός / δυνατή / δυνατό = strong, loud
• adverb: δυνατά = loudly

Here it means very.

That is because it is modifying the adverb δυνατά:

• πολύ δυνατά = very loudly

Greek πολύ can mean either very or a lot, depending on what it modifies:

• μιλάει πολύ = she talks a lot
• μιλάει πολύ δυνατά = she speaks very loudly

So the context tells you which meaning is intended.

Greek word order is more flexible than English word order.

In this sentence, στην κερκίδα comes right after η οπαδός, so it naturally sounds like it is describing which fan:

• Η οπαδός στην κερκίδα = the fan in the stands

Then the sentence tells you what she is doing:

• μιλάει πολύ δυνατά = speaks very loudly

If you moved it, the meaning would still be similar, but the focus could shift a little. For example:

• Η οπαδός μιλάει πολύ δυνατά στην κερκίδα

This can sound more like the location of the action: she is speaking very loudly in the stands.

Because Greek uses articles very regularly. Each noun phrase gets its own article if it is definite.

Here you have:

• η οπαδός = the fan
• στην κερκίδα = in the stands / in the stand

Notice that the second article is hidden inside στην, since στην = σε + την.

This is normal Greek structure. Greek generally uses the definite article more often than English does.

A rough pronunciation guide is:

ee o-pa-DHOS steen ker-KEE-dha mee-LA-ee po-LEE dhi-na-TA

A few helpful notes:

• η sounds like ee
• δ sounds like the th in this
• ει in μιλάει sounds like ee
• the accent mark shows which syllable is stressed

So the stressed parts are:

• οπαδός
• κερκίδα
• μιλάει
• πολύ
• δυνατά

If you want to sound natural, make sure those stressed syllables stand out clearly.