Я купил эти джинсы на распродаже.

This is about aspect, which is very important in Russian verbs.

• купить → perfective
• покупать → imperfective

Купил is the past tense of the perfective verb купить, and it usually means the action is seen as completed: the speaker successfully bought the jeans.

So in this sentence, Я купил эти джинсы... means something like:

• I bought these jeans
• the purchase happened and is finished

If you used покупал, it would sound more like:

• I was buying
• I used to buy
• I bought with focus on the process rather than the completed result

In a simple statement about a finished purchase, купил is the natural choice.

In Russian, the past tense is usually formed with -л plus endings that show gender and number.

For купить, the past tense forms are:

• купил — masculine singular
• купила — feminine singular
• купило — neuter singular
• купили — plural

So Я купил tells you the speaker is male.

If the speaker were female, it would be:

• Я купила эти джинсы на распродаже.

This is something English does not do, so it often stands out to learners.

Not completely.

In the Russian past tense, the verb shows gender and number, but not person. So купил by itself does not specifically mean I bought. Depending on context, it could mean:

• I bought (if the speaker is male)
• you bought (talking to one male person)
• he bought

That is why Я is useful here: it makes the subject explicit.

Compare:

• Я купил — I bought
• Он купил — he bought
• Ты купил — you bought (to one male)

So unlike present-tense forms such as я покупаю, the past tense form alone does not identify the person.

Эти is the plural form of этот (this / these).

Here it agrees with джинсы, which is:

• plural
• inanimate
• the direct object of the verb

Because джинсы is an inanimate plural noun, its accusative plural form looks the same as the nominative plural form. That is why you get:

• эти джинсы

The same form could also be nominative plural, but here the role in the sentence shows it is the object.

A useful comparison:

• Я вижу эти джинсы. — inanimate plural object
• Я вижу этих людей. — animate plural object

For animate plural nouns, the accusative changes differently.

Джинсы is a plural-only noun in normal usage, like English jeans, pants, or scissors in some contexts.

So Russian usually treats one pair of jeans as grammatically plural:

• эти джинсы
• новые джинсы
• мои джинсы

If you need to be extra precise, you can say:

• пара джинсов — a pair of jeans

Notice that after пара, the noun changes:

• пара джинсов

But in everyday speech, just джинсы is completely normal.

Because джинсы here is an inanimate direct object.

In Russian, the accusative behaves differently depending on whether the noun is animate or inanimate:

• inanimate plural accusative = same as nominative plural
• animate plural accusative = same as genitive plural

So:

• Я купил эти джинсы. — inanimate, so эти джинсы
• Я видел этих студентов. — animate, so этих студентов

That is why the form stays эти джинсы here.

This is mostly an idiomatic preposition choice.

Russian often uses на with events, activities, and some commercial situations where English might use at, in, or even no preposition at all. So:

• на распродаже = at a sale, in a sale, or often just on sale depending on context

Here, на распродаже is the natural expression.

Some similar examples:

• на концерте — at the concert
• на выставке — at the exhibition
• на уроке — in class / at the lesson

So this is a phrase you should mostly learn as a set expression: купить что-то на распродаже.

Распродаже is in the prepositional case.

That is because after на when it means location, setting, or context, Russian often uses the prepositional case.

Basic pattern:

• на + prepositional

So:

• распродажа — dictionary form, nominative singular
• на распродаже — prepositional singular

This ending -е is very common for feminine nouns in the prepositional singular.

It can suggest either idea, depending on context.

In this sentence, Я купил эти джинсы на распродаже, the phrase usually means the jeans were bought:

• at a sale
• during a sale
• effectively on sale

So the emphasis is that the purchase happened in the context of a discount sale.

If you want to focus more specifically on the discount itself, Russian might also use expressions like:

• со скидкой — with a discount
• по скидке — less standard in some contexts, often avoided by learners
• по акции — as part of a promotion

But на распродаже is a very natural and common way to say it.

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

The neutral order here is:

• Я купил эти джинсы на распродаже.

But you can also say:

• Эти джинсы я купил на распродаже.
• На распродаже я купил эти джинсы.

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

For example:

• Эти джинсы я купил на распродаже puts more emphasis on these jeans
• На распродаже я купил эти джинсы puts more emphasis on the sale

So Russian word order often reflects information focus rather than strict grammatical necessity.

Russian does not have articles like a/an and the.

So Russian simply says:

• Я купил эти джинсы на распродаже.

Definiteness is understood from context or shown in other ways, such as:

• demonstratives like этот / эта / это / эти — this / these
• word order
• context

Here, эти already helps make the noun specific: these jeans.

So Russian does not need a separate word for the.

A natural pronunciation would be something like:

• Я купи́л э́ти джи́нсы на распрода́же.

Stress:

• купи́л
• э́ти
• джи́нсы
• распрода́же

A few pronunciation notes:

• я is usually pronounced quickly
• купи́л has stress on the second syllable
• дж in джинсы sounds like the j in jam
• распрода́же has stress on -да́-

Listening practice is especially helpful here, because Russian vowel reduction in unstressed syllables can make the spoken form sound different from the spelling.