Моя сестра хочет дрессировать щенка сама, чтобы он не тянул поводок на улице.

Because сестра is a feminine singular noun, and the possessive pronoun has to agree with it.

• мой брат = my brother
• моя сестра = my sister
• моё письмо = my letter
• мои друзья = my friends

So моя сестра means my sister.

Because сестра is the subject of the sentence — the person doing the wanting.

The structure is:

• Моя сестра = the subject
• хочет дрессировать = wants to train

So nominative is used because she is the one performing the action.

After хотеть (to want), Russian normally uses an infinitive to say what someone wants to do.

So:

• хочет = wants
• дрессировать = to train

Together: хочет дрессировать = wants to train

This is a very common pattern:

• Я хочу спать. = I want to sleep.
• Он хочет есть. = He wants to eat.
• Она хочет работать. = She wants to work.

Yes. Дрессировать is the standard verb for training an animal, especially a dog.

So дрессировать щенка means to train a puppy.

A learner should note that this verb is usually used for animals, not people. For people, Russian would use different verbs depending on context, such as:

• тренировать = to coach/train physically
• обучать = to teach
• воспитывать = to raise/bring up

For a dog or puppy, дрессировать is exactly the natural choice.

Because щенок is the direct object of дрессировать, so it should be in the accusative case.

But there is an extra detail: щенок is a masculine animate noun. In Russian, masculine animate nouns have an accusative form that looks like the genitive.

So:

• nominative: щенок
• accusative: щенка

Compare:

• Я вижу стол. = I see a table. (inanimate, accusative = nominative)
• Я вижу щенка. = I see a puppy. (animate, accusative = genitive-like form)

Сама means herself or on her own, and it adds emphasis.

Here it means that the sister wants to train the puppy herself, rather than having someone else do it.

It agrees with сестра, so it is feminine singular:

• сам = masculine
• сама = feminine
• само = neuter
• сами = plural

So:

• Моя сестра хочет дрессировать щенка сама = My sister wants to train the puppy herself.

Yes. Russian word order is flexible, and moving сама changes the emphasis a little.

For example:

• Моя сестра хочет дрессировать щенка сама.
• Моя сестра сама хочет дрессировать щенка.
• Сама моя сестра хочет дрессировать щенка. — less neutral, more marked

The version in your sentence sounds natural and emphasizes that she wants to do the training herself.

Чтобы introduces a clause of purpose here. It means something like:

• so that
• in order that

So:

• ..., чтобы он не тянул поводок на улице. = ..., so that he won’t pull on the leash outside.

This tells us the goal of the training.

After чтобы, Russian often uses a verb form that looks like the past tense, but it does not mean past time here.

So чтобы он не тянул means:

• so that he would not pull
• so that he doesn’t pull
• so that he won’t pull

This is a very common Russian pattern:

• Я пришёл, чтобы помочь. = I came to help.
• Она говорит медленно, чтобы дети понимали. = She speaks slowly so that the children understand.

Here тянул is masculine singular because it agrees with он.

Because the subject changes.

In the first part, the subject is моя сестра.

In the purpose clause, the subject is он — the puppy.

So Russian includes the pronoun to make that clear:

• Моя сестра хочет дрессировать щенка сама, чтобы он не тянул поводок...

Without он, the sentence would be incomplete or unclear, because the second clause needs its own subject.

Because it agrees with он, which refers to щенок.

In чтобы clauses, the verb often uses a form that looks like the past tense, and past-tense forms in Russian show gender and number:

• он тянул
• она тянула
• оно тянуло
• они тянули

Since щенок is masculine, the sentence uses он не тянул.

Russian expresses this a bit differently. The leash is treated as a direct object, so Russian says:

• тянуть поводок = literally to pull the leash

This is the normal way to say that a dog pulls on the leash while walking.

So although English often uses pull on the leash, Russian naturally uses тянуть поводок.

Поводок means leash.

It is a masculine noun:

• nominative: поводок
• accusative: поводок (same here because it is inanimate)

So:

• тянуть поводок = to pull the leash

Because поводок is inanimate, while щенок is animate.

Both are masculine nouns, but in the accusative singular:

• animate masculine nouns usually change form:
  • щенок → щенка
• inanimate masculine nouns usually stay the same:
  • поводок → поводок

So the difference comes from animacy, which is very important in Russian grammar.

На улице means outside, out on the street, or when out walking.

Literally it is on the street, but in many contexts Russian uses на улице more broadly to mean outdoors.

So here:

• чтобы он не тянул поводок на улице = so that he doesn’t pull on the leash outside / when out on walks

Yes, but it would change the nuance.

Дрессировать is imperfective, so it focuses on the process of training.

That fits well here, because training a puppy is an ongoing activity.

A perfective verb such as выдрессировать would focus more on the result — training the puppy successfully/completely.

So:

• хочет дрессировать щенка = wants to train the puppy
• хочет выдрессировать щенка = wants to get the puppy fully trained

The imperfective version in your sentence sounds very natural.

Because the sentence is talking about a general repeated behavior the sister wants to prevent.

• тянуть поводок = to pull on the leash habitually / as a behavior

If you used a perfective verb, it could sound more like one single completed act of pulling, which is not the main idea here.

The point is not one tug, but the ongoing problem of the puppy pulling during walks. That is why не тянул works well.

No. They are different.

• сама / сам / сами = self, used for emphasis: herself / himself / themselves
• себя = the reflexive pronoun oneself

In this sentence, сама is emphatic:

• Моя сестра хочет дрессировать щенка сама = My sister wants to train the puppy herself.

But себя is used when the action comes back to the subject:

• Она видит себя в зеркале. = She sees herself in the mirror.

So сама here is the correct word, not себя.

Yes, it is natural and idiomatic.

A native speaker would understand it as:

My sister wants to train the puppy herself so that it doesn’t pull on the leash outside.

The grammar, vocabulary, and word order all work well in normal Russian.