Ο βοηθός είναι εδώ.

Ο is the definite article, meaning the. In this sentence it is the masculine singular nominative form, because βοηθός is the subject.

It is capitalized only because it is the first word of the sentence. In the middle of a sentence, it would normally be ο.

Not necessarily. Βοηθός can refer to either a man or a woman. The article tells you the gender here:

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

So in Ο βοηθός είναι εδώ, the article ο shows that the assistant is male.

Είναι is the present-tense form of είμαι, meaning to be. Here it means is.

So the structure is:

• Ο βοηθός = the assistant
• είναι = is
• εδώ = here

A useful extra point: είναι is also the form for are with they, so context tells you whether it is singular or plural.

In a normal full sentence like this, no. Greek normally keeps είναι:

• Ο βοηθός είναι εδώ.

If you remove it and say Ο βοηθός εδώ, it sounds incomplete in standard Greek. You may see omissions in headlines, notes, or very informal speech, but for normal sentence building, keep είναι.

The sentence is perfectly natural as it is, but Greek word order is fairly flexible.

For example:

• Ο βοηθός είναι εδώ. = neutral statement
• Εδώ είναι ο βοηθός. = more focus on here, or a slight sense of Here is the assistant
• Είναι εδώ ο βοηθός. = possible, but more marked and context-dependent

So yes, the order can change, but Ο βοηθός είναι εδώ is the most straightforward version.

A rough pronunciation is:

o voi-THOS EE-ne e-THO

A few helpful sound notes:

• β sounds like v, not English b
• θ sounds like th in think
• δ sounds like th in this
• εί / η / ι / ει all sound like ee in Modern Greek

Stress falls where the accent mark is:

• βοηθός → stress on the last syllable
• είναι → stress on the first syllable
• εδώ → stress on the second syllable

In Modern Greek, the accent mark shows which syllable is stressed.

So:

• βοηθός → stress the last syllable
• είναι → stress the first syllable
• εδώ → stress the last syllable

These accents are a normal part of spelling, not optional pronunciation hints. They are important to learn early, because stress matters in Greek.