Наставник помог мне.

Because the verb помочь / помогать takes the dative case for the person who receives the help.

So:

• я = I (nominative)
• меня = me (accusative/genitive)
• мне = to me / me in the dative

Russian asks помочь кому? = to help whom?
Answer: мне.

So Наставник помог мне is grammatically The mentor helped me, but the structure is closer to helped to me.

Помог is the past tense, masculine singular form of the verb помочь.

Key points:

• помочь = perfective infinitive, to help
• помог = helped / did help / helped successfully

It describes a completed action.

Compare:

• Наставник помог мне. = The mentor helped me.
• Наставник помогал мне. = The mentor was helping me / used to help me.

The second sentence uses the imperfective verb помогать.

This verb changes stem forms. That is normal for помочь.

Some important forms are:

• infinitive: помочь
• past masculine: помог
• past feminine: помогла
• past plural: помогли

So yes, it is a form you mainly have to learn as part of the verb’s pattern. Russian has several common verbs with stem changes like this.

Наставник is in the nominative case, which is the usual case for the subject of a sentence.

In this sentence:

• Наставник = subject
• помог = verb
• мне = indirect object in the dative

So the structure is:

Наставник | помог | мне
subject | verb | person helped

In the past tense, Russian verbs agree with the subject in gender and number.

Here:

• помог = masculine singular
• помогла = feminine singular
• помогло = neuter singular
• помогли = plural

So помог tells you that the subject is grammatically masculine singular. That matches наставник, which is a masculine noun.

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

All of these are possible:

• Наставник помог мне.
• Мне помог наставник.
• Помог мне наставник.

The basic meaning stays the same, but the focus changes:

• Наставник помог мне. = neutral
• Мне помог наставник. = emphasizes me
• Помог мне наставник. = more marked or stylistic

For learners, Наставник помог мне is the safest neutral order.

Russian does not have articles like a or the.

So наставник can mean:

• a mentor
• the mentor

Context tells you which one is meant.

But it does not automatically mean my mentor. If you want that, you usually say:

• Мой наставник помог мне. = My mentor helped me.

A helpful pronunciation guide is:

• наставник = na-STAV-nik
• помог = pa-MOK
• мне = roughly mnye

With stress marks:

• настА́вник помог м

не́? Wait, мне is one syllable and may or may not carry sentence stress depending on context.

• More clearly for word stress:
  • настА́вник
  • помО́г
  • мне

A few pronunciation notes:

• In помог, final г is pronounced like k at the end of the word, so it sounds like памók / pa-MOK.
• мне begins with the consonant cluster mn-, which can feel unusual for English speakers.

Because Russian past tense is usually expressed with just one verb form.

So:

• помог = helped

Russian does not need an auxiliary here like English sometimes does.

Compare:

• English: The mentor helped me.
• Russian: Наставник помог мне.

Just one past-tense verb is enough.

Usually, yes. Because помочь is perfective, it normally presents the help as a completed event or a successful result.

If you want to describe:

• an ongoing process,
• repeated help,
• or general habitual help,

you would often use помогать instead:

• Наставник помогал мне. = The mentor was helping me / used to help me.

So in your sentence, the speaker is presenting the help as a finished act.