Я купил набор инструментов.

Купил is the masculine singular past tense form of the verb купить (to buy, perfective).

• купил = he bought / I bought if the speaker is male
• купила = the speaker is female
• покупал / покупала comes from покупать, the imperfective verb, which usually focuses on the process, repetition, or background action

In this sentence, купил is natural because it presents the purchase as a completed event: I bought a set of tools.

So:

• male speaker: Я купил набор инструментов.
• female speaker: Я купила набор инструментов.

In Russian, the past tense is formed in a way that reflects gender and number, not person.

So in the past tense:

• я купил = I bought (male speaker)
• я купила = I bought (female speaker)
• мы купили = we bought

This is different from English, where I bought stays the same regardless of gender.

Набор is in the accusative case.

That is because it is the direct object of the verb купил: you bought what? → набор.

However, набор is a masculine inanimate noun, and for masculine inanimate nouns, the accusative singular looks the same as the nominative singular.

So:

• nominative: набор
• accusative: набор

That is why its form does not change here.

Because after набор (a set, a collection), Russian usually uses the noun that follows in the genitive plural.

So:

• набор чего? = a set of what?
• инструментов = of tools

This is a very common pattern:

• стакан воды = a glass of water
• чашка чая = a cup of tea
• набор ключей = a set of keys
• группа студентов = a group of students

So набор инструментов literally means a set of tools, where инструментов is genitive plural.

The dictionary form is инструмент (tool, singular).

Its plural nominative is:

• инструменты = tools

Its plural genitive is:

• инструментов = of tools

In this sentence, набор requires the meaning set of tools, so Russian uses the genitive plural: инструментов.

Yes, often you can.

Russian frequently omits subject pronouns when they are clear from context. So:

• Я купил набор инструментов.
• Купил набор инструментов.

Both can mean I bought a set of tools, depending on context.

However, Я may be included:

• for emphasis
• for contrast
• to make the sentence clearer

For example:

• Я купил набор инструментов, а он купил дрель. = I bought a set of tools, and he bought a drill.

No, Russian word order is more flexible than English word order.

The neutral order here is:

• Я купил набор инструментов.

But other orders are possible, depending on emphasis:

• Набор инструментов я купил. = It was a set of tools that I bought.
• Купил я набор инструментов. = can sound marked, emotional, or contrastive depending on context

Even though Russian word order is flexible, the basic subject–verb–object order is the safest and most neutral for learners.

Купить is perfective.

Russian verbs often come in aspect pairs:

• покупать = imperfective
• купить = perfective

The perfective aspect is used when the action is seen as:

• completed
• one whole event
• producing a result

Here, the result matters: the person successfully bought the tool set. That is why купил is natural.

Compare:

• Я покупал набор инструментов. = I was buying / I used to buy / I bought (with focus on process or experience, depending on context)
• Я купил набор инструментов. = I bought a set of tools (completed purchase)

The stress is:

• Я купи́л набор инструментов.

So:

• купи́л
• набо́р
• инструме́нтов

Approximate pronunciation:

• ya koo-PEEL na-BOR een-stroo-MYEN-tuf

A few details:

• unstressed о is reduced in pronunciation
• final в in инструментов is often pronounced closer to f in actual speech

Yes, набор инструментов is a very natural and common way to say tool set or set of tools.

Depending on context, Russian can also use:

• комплект инструментов = a set/kit of tools
• ящик с инструментами = a toolbox / box with tools

But for the simple meaning a tool set, набор инструментов is perfectly normal.

Yes. Like English instrument or tool, Russian инструмент can have both a literal and a figurative meaning.

Literal:

• hammer, wrench, screwdriver, etc.

Figurative:

• политический инструмент = a political tool
• инструмент анализа = a tool for analysis

But in набор инструментов, the default interpretation is usually a physical tool set, unless the context suggests something abstract.

Russian has no articles like English a and the.

So:

• набор инструментов can mean a set of tools or the set of tools

Which one is meant depends on context.

In this sentence, the natural English translation is usually I bought a set of tools, but Russian itself does not explicitly mark a or the.

The dictionary forms are:

• я = I
• купить = to buy (perfective)
• набор = set, kit, collection
• инструмент = tool, instrument

The sentence form is:

• Я = unchanged
• купил = past masculine singular of купить
• набор = accusative singular
• инструментов = genitive plural of инструмент