Ο βοηθός ελέγχει τη μονάδα.

• Ο βοηθός = the subject of the sentence
• ελέγχει = the verb
• τη μονάδα = the direct object

So the structure is the very common Greek pattern:

Subject + Verb + Object

Ο is the masculine singular definite article in the nominative case.
It means the.

Here it goes with βοηθός, so ο βοηθός means the assistant.

Greek articles change form depending on:

• gender
• number
• case

So Greek uses different forms of the, unlike English.

No. βοηθός can refer to a male or a female assistant. The article tells you which one is meant here.

• ο βοηθός = the male assistant
• η βοηθός = the female assistant

So in this sentence, because it says ο βοηθός, it refers to a male assistant.

This is a very useful thing to notice in Greek: sometimes the noun stays the same, and the article shows the gender.

Because μονάδα is the object of the verb, not the subject.

• η μονάδα = nominative form, used for the subject
• τη μονάδα = accusative form, used for the direct object

Since the sentence says that the assistant is checking the unit, μονάδα is receiving the action, so Greek uses the accusative article: τη.

English does not show this kind of change in the, but Greek does.

The full accusative feminine singular article is την, but in everyday Modern Greek the final -ν is often dropped before certain consonants.

So:

• την μονάδα is the full form
• τη μονάδα is the usual shortened form here

Before μ in μονάδα, dropping the -ν is normal.

You should recognize both forms, but τη μονάδα is completely standard.

ελέγχει is:

• present tense
• 3rd person singular
• from the verb ελέγχω = to check / inspect / control

So it means:

• he checks
• she checks
• it checks

Here, because the subject is ο βοηθός, it means the assistant checks.

A useful mini-pattern:

• εγώ ελέγχω = I check
• εσύ ελέγχεις = you check
• αυτός/αυτή/αυτό ελέγχει = he/she/it checks

It can mean either, depending on context.

Greek present tense often covers both:

• he checks
• he is checking

So Ο βοηθός ελέγχει τη μονάδα could be understood as:

• The assistant checks the unit
• The assistant is checking the unit

Usually the wider context tells you which is more natural.

A rough pronunciation guide is:

o vo-i-THOS e-LE-nghi ti mo-NA-tha

A few helpful points:

• β sounds like v
• θ sounds like th in thin
• δ sounds like th in this
• γχ in ελέγχει is pronounced roughly like ngh / nghy
• the stress marks show which syllable gets the emphasis:
  • βοηθός
  • ελέγχει
  • μονάδα

A more careful approximation is:

[o vo.iˈθos eˈleŋçi ti moˈnaða]

Yes. Greek word order is more flexible than English.

The neutral, basic order here is:

Ο βοηθός ελέγχει τη μονάδα.

But Greek can also move parts around for emphasis, for example:

• Τη μονάδα ελέγχει ο βοηθός.

That still means basically the same thing, but it puts more focus on the unit.

So while Subject + Verb + Object is the normal starting pattern for learners, Greek is not as rigid as English.

Because it is a feminine noun, and you can see that from its article and form:

• η μονάδα = nominative singular feminine
• τη μονάδα = accusative singular feminine

Many Greek nouns ending in -α are feminine, though you should not assume this is true in every single case.

Here the feminine article agrees with the noun:

• τη matches μονάδα

Agreement is very important in Greek.

Yes, but the meaning changes slightly.

Ελέγχει τη μονάδα means:

• He/she is checking the unit or
• He/she checks the unit

Greek often leaves out subject pronouns because the verb ending already gives person and number.

However, if you want to specify who is doing the action, you keep the noun:

• Ο βοηθός ελέγχει τη μονάδα.

So the full sentence is more explicit.

The accent marks show which syllable is stressed.

In this sentence:

• βοηθός → stress on -θός
• ελέγχει → stress on λέγ
• μονάδα → stress on νά

Stress matters in Greek pronunciation, so learners should pay attention to the written accent.

It is not optional spelling decoration: it tells you how to say the word correctly.