Mój przyjaciel pomoże ci.

Because mój has to agree with przyjaciel.

• przyjaciel is masculine singular
• so the possessive pronoun must also be masculine singular nominative: mój

Compare:

• mój przyjaciel = my male friend
• moja przyjaciółka = my female friend
• moje dziecko = my child

So mój does not depend on the speaker’s gender. It depends on the noun it describes.

Specifically, przyjaciel is a male friend.

Polish usually marks gender in nouns like this:

• przyjaciel = male friend
• przyjaciółka = female friend

So if you are talking about a woman who is your friend, you would normally say moja przyjaciółka.

Also, przyjaciel often suggests a fairly close friend, not just an acquaintance.

Pomoże is the 3rd person singular form of the verb pomóc.

So:

• dictionary form: pomóc = to help
• pomoże = he/she/it will help

In this sentence, the subject is mój przyjaciel, so pomoże means my friend will help.

This is because pomóc is a perfective verb.

In Polish, perfective verbs do not normally have a true present tense. Their present-looking forms refer to the future.

So:

• pomaga = helps / is helping / does help
  from pomagać (imperfective)
• pomoże = will help
  from pomóc (perfective)

That means pomoże is naturally translated as will help, not helps.

Because ty is the subject form, meaning you as the person doing the action.

But here you is the person receiving the help, not doing it. Polish uses the dative case after pomóc.

So:

• ty = you (subject)
• ci / tobie = to you

The verb works like this:

• pomóc komu? = to help whom?
• answer: ci = to you

So Mój przyjaciel pomoże ci literally works like My friend will help to-you.

Both can mean to you here.

• ci = short, unstressed form
• tobie = full, more emphatic form

In a neutral sentence, ci is very common:

• Mój przyjaciel pomoże ci.

If you want emphasis or contrast, tobie is more likely:

• Mój przyjaciel pomoże tobie, nie mnie.
  = My friend will help you, not me.

So in this sentence, ci is the normal everyday choice.

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

English usually needs a subject pronoun:

• He will help you

Polish often does not:

• Pomoże ci = He/She/It will help you

In your sentence, the subject is already stated as mój przyjaciel, so adding on would be unnecessary unless you wanted special emphasis:

• On ci pomoże = He will help you

Yes. Polish word order is much more flexible than English word order.

The neutral version is:

• Mój przyjaciel pomoże ci.

But you may also hear:

• Mój przyjaciel ci pomoże.
• Ci pomoże mój przyjaciel.
• Pomoże ci mój przyjaciel.

These all keep roughly the same basic meaning, but the emphasis changes.

A useful thing to remember is that short pronouns like ci often avoid strong stress and often appear near the verb.

A rough English-style guide would be:

• mój ≈ mooy
• przyjaciel ≈ pshih-YA-chel
• pomoże ≈ po-MO-zheh
• ci ≈ a soft chee

More exactly:

• mój = /muj/
• przyjaciel = /pʂɨˈja.t͡ɕel/
• pomoże = /pɔˈmɔ.ʐɛ/
• ci = /t͡ɕi/

Stress is usually on the second-to-last syllable:

• przyJAciel
• poMOże

Yes, but it would not mean exactly the same thing.

• Mój przyjaciel pomoże ci = My friend will help you
• Przyjaciel pomoże ci = A/The friend will help you, depending on context

Because Polish has no articles like a and the, context decides the exact meaning. If you want to clearly say my friend, keep mój.

Yes. Ci here is the singular informal you, used with someone you address as ty.

If you were speaking formally, Polish would use a different structure, for example:

• Mój przyjaciel pomoże panu. = My friend will help you, sir
• Mój przyjaciel pomoże pani. = My friend will help you, ma’am

So the original sentence sounds informal and friendly.

Normally, no.

Przyjaciel means male friend, not boyfriend. For boyfriend, Polish usually uses:

• chłopak
• sometimes partner, depending on context

So mój przyjaciel is best understood as my male friend.

It is in the nominative case because it is the subject of the sentence.

You can see the structure like this:

• Mój przyjaciel = subject, nominative
• pomoże = verb
• ci = indirect object, dative

So the grammar is:

• Who will help? → mój przyjaciel
• Whom will he help? → ci