Когда я вернусь домой, я покормлю собаку.

Вернусь is the 1st person singular future form of вернуться (to come back / return).

A few useful points:

• вернуться is a perfective verb, so its “present-looking” forms actually refer to the future.
• That means я вернусь = I will return / I’ll come back.
• возвращусь also exists, from возвратиться / возвращаться, but вернуться is usually more common and natural in everyday speech for this idea.

So in this sentence, Когда я вернусь домой... means When I return home... / When I come back home...

That is a very common English-speaker question.

In Russian, when a future event is meant, it is normal to use a future form in the когда clause:

• Когда я вернусь домой, ... = When I return home, ...

English normally avoids will after when, but Russian does not follow that rule. Russian simply states the event as future.

So although English says:

• When I get home, I’ll feed the dog

Russian says:

• Когда я вернусь домой, я покормлю собаку.

This is fully normal Russian.

This is about aspect.

• покормлю comes from покормить, a perfective verb.
• буду кормить is the future of the imperfective verb кормить.

The perfective покормлю presents the action as a single completed event:

• I will feed the dog = one whole action, done after I get home.

If you said буду кормить, it would focus more on the process or duration:

• I will be feeding the dog
• or I’ll feed the dog with emphasis on the activity itself, not its completion

In this sentence, the speaker probably means a simple completed action: first I get home, then I feed the dog. That is why покормлю fits well.

They are related but differ in aspect and nuance.

• кормить = to feed, to be feeding, to feed regularly
  This is imperfective.
• покормить = to feed (once / as a completed action)
  This is perfective.

Examples:

• Я кормлю собаку каждый день.
  I feed the dog every day.
  Repeated/habitual action → imperfective

• Я покормлю собаку.
  I’ll feed the dog.
  One completed future act → perfective

So по- here helps create the perfective partner meaning to do the feeding and complete it.

Because Когда я вернусь домой is a subordinate clause, and Russian normally separates subordinate clauses from the main clause with a comma.

Structure:

• Когда я вернусь домой, = subordinate time clause
• я покормлю собаку. = main clause

So the comma is required.

This is similar to English punctuation in:

• When I get home, I’ll feed the dog.

Домой means homeward / to home / home and is used with verbs of motion.

So:

• вернуться домой = to return home
• идти домой = to go home

Compare:

• дома = at home
• к дому = toward the house / up to the house

Examples:

• Я дома. = I am at home.
• Я иду домой. = I am going home.
• Я подхожу к дому. = I am approaching the house.

So домой is exactly the right form after вернусь.

Because собаку is the accusative case, used for the direct object of the verb покормлю.

The speaker is feeding the dog, so dog is the object.

The dictionary form is:

• собака = dog

But as a feminine noun in the accusative singular:

• собака → собаку

Also, since собака refers to an animate being, the accusative matters especially in Russian patterns of object marking.

So:

• Я покормлю собаку. = I will feed the dog.

Yes, the second я can be omitted.

You can say:

• Когда я вернусь домой, покормлю собаку.

This is natural because the subject is clearly the same in both clauses.

But repeating я is also perfectly correct:

• Когда я вернусь домой, я покормлю собаку.

Repeating it can make the sentence feel:

• a bit clearer
• slightly more explicit
• sometimes a little more emphatic

So both versions are good. Russian often allows subject pronouns to be omitted when the verb form already shows who is doing the action.

Yes. Russian word order is flexible, though the neutral version here is very natural.

Neutral order:

• Когда я вернусь домой, я покормлю собаку.

Possible variants:

• Я покормлю собаку, когда вернусь домой.
• Когда вернусь домой, покормлю собаку.

These all mean basically the same thing, but the emphasis can shift a little.

For example:

• Я покормлю собаку, когда вернусь домой may put slightly more focus on what I’ll do
• Когда вернусь домой, покормлю собаку sounds a bit more compact and conversational

So the original sentence is standard, but not the only possible word order.

They are similar, but not always identical in nuance.

• вернуться домой = to return home / come back home
• прийти домой = to come home / arrive home

If the idea is specifically coming back, then вернуться is better. If the focus is just arriving home, прийти домой may be enough.

Compare:

• Когда я вернусь домой, я покормлю собаку.
  When I return home, I’ll feed the dog.
• Когда я приду домой, я покормлю собаку.
  When I come home / arrive home, I’ll feed the dog.

Both are possible, but вернусь suggests more clearly that the person is coming back from somewhere.

Both verbs are 1st person singular because the speaker is talking about I.

• вернусь = I will return
• покормлю = I will feed

You can see this from the verb endings:

• -усь in вернусь
• -ю in покормлю

Both correspond to я.

So the sentence is entirely in the first person singular future.

Not naturally in this exact form.

Because both verbs are perfective:

• вернусь
• покормлю

the sentence most naturally refers to one future occasion:

• When I get home, I’ll feed the dog.

If you wanted a habitual meaning such as Whenever I come home, I feed the dog, Russian would more likely use imperfective verbs and often a slightly different structure, for example:

• Когда я возвращаюсь домой, я кормлю собаку.

That suggests a repeated or usual action.

So the original sentence is best understood as a single future sequence.

Yes. The sentence shows a very common Russian pattern: one future action happens after another.

Sequence:

1. Когда я вернусь домой = first, I get back home
2. я покормлю собаку = then, I feed the dog

Because both verbs are perfective, the sentence sounds neat and goal-oriented:

• one event is completed
• then the next event is completed

This is a very typical way Russian expresses future plans or intentions with a clear order of events.