Η διαλογή αρχίζει τώρα.

Yes. Η is the feminine singular definite article, so here it means the.

A few useful points:

• It is capitalized because it is the first word of the sentence.
• Even though it looks like the English letter H, in Modern Greek it is pronounced ee.
• Its lowercase form is η.

So Η διαλογή = the sorting / the selection, depending on context.

Yes. διαλογή is a feminine noun, so it takes the feminine article η in the nominative singular.

How you can tell:

• The article η marks feminine singular nominative.
• Many nouns ending in -ή are feminine.

In this sentence, η διαλογή is the subject, so nominative singular is exactly what you would expect.

It is in the nominative singular.

Why:

• It is the subject of the sentence.
• The verb αρχίζει means begins / is beginning, and the thing doing that is η διαλογή.

So the structure is basically:

• η διαλογή = the subject
• αρχίζει = the verb
• τώρα = now

Because αρχίζει is the third person singular form of the verb αρχίζω.

That matches the subject:

• αρχίζω = I begin
• αρχίζεις = you begin
• αρχίζει = he/she/it begins

Since η διαλογή is a singular thing, Greek uses αρχίζει.

It is the present tense.

In English, the best translation depends on context:

• begins now
• is beginning now
• starts now

With τώρα meaning now, it often sounds like an announcement of something starting immediately.

So Greek present tense here can overlap with both simple and progressive English.

Because Greek does not build the present progressive the same way English does.

English often uses:

• is beginning

Greek can simply use the present tense:

• αρχίζει

So one Greek form can cover what English expresses as either:

• begins
• is beginning

That is very normal in Modern Greek.

The accent mark shows which syllable is stressed.

So:

• διαλογή → stress on the last syllable
• αρχίζει → stress on the middle syllable
• τώρα → stress on the first syllable

A rough guide:

• δια-λο-ΓΗ
• αρ-ΧΙ-ζει
• ΤΩ-ρα

In Modern Greek, written accents are important because they tell you where to place the stress.

A rough pronunciation guide is:

ee thya-lo-YEE ar-HEE-zee TO-ra

A few sound notes:

• η = ee
• δ = the th in this, not in think
• γ before ι/η/ε/αι often sounds like y
• χ before ι/η/ε is a softer sound, somewhat like the h in human for many English speakers, though the real Greek sound is stronger
• τώρα = TO-ra

If you want to sound natural, stress matters a lot:

• διαλογή
• αρχίζει
• τώρα

Yes, it could move.

Greek word order is more flexible than English. This sentence uses a very natural order:

• Η διαλογή αρχίζει τώρα.

But you could also hear:

• Τώρα αρχίζει η διαλογή.
• Η διαλογή τώρα αρχίζει.

The meaning stays basically the same, but the emphasis shifts:

• Τώρα αρχίζει η διαλογή emphasizes now
• Η διαλογή αρχίζει τώρα is a neutral, straightforward statement

In normal Greek, the article is usually expected here.

So:

• Η διαλογή αρχίζει τώρα sounds natural.

Without the article:

• Διαλογή αρχίζει τώρα

that would sound odd in most everyday contexts.

Greek uses the definite article more often than English does, especially with subjects and many abstract or general nouns.

It can vary by context.

Depending on the situation, διαλογή can mean things like:

• sorting
• selection
• picking out
• screening

So the exact English word depends on what is being discussed:

• mail, objects, materials → often sorting
• candidates, items, options → often selection

That is why context matters even if the grammar stays the same.