Когда дома заканчивается корм, я сразу иду в зоомагазин после работы.

Когда here means when/whenever, not just a one-time when.

In this sentence, it describes a regular situation:

• Когда дома заканчивается корм... = Whenever we run out of pet food at home...

If you used если, the meaning would shift more toward if:

• Если дома заканчивается корм... = If we run out of pet food at home...

That can be possible in some contexts, but когда is more natural if the speaker means this is the usual pattern: this happens, and then I do that.

Дома is a very common adverb meaning at home.

So:

• дома = at home
• домой = to home / homeward
• в доме = in the house/building

In this sentence:

• Когда дома заканчивается корм... = When the pet food runs out at home...

That sounds natural because the speaker is talking about the household situation, not literally about something being physically located inside a building.

Корм means feed or pet food, depending on context.

In everyday speech, especially with pets, корм often means:

• dry food
• canned pet food
• animal feed in general

So in зоомагазин context, корм is most naturally understood as pet food.

It is a mass noun here, like English food or feed, so Russian does not need to specify plural:

• заканчивается корм = the pet food is running out / has run out

Заканчивается comes from заканчиваться / закончиться, which means to come to an end, to run out, to be used up.

The -ся here does not mean a literal reflexive action like wash oneself. In many verbs, -ся creates an intransitive meaning:

• заканчивать что-то = to finish something
• заканчиваться = to finish / come to an end / run out

Compare:

• Я заканчиваю работу. = I finish the work.
• Работа заканчивается. = The work is ending.

So:

• заканчивается корм = the pet food runs out / is running out

Russian often uses the present tense in clauses with когда to describe habitual repeated situations.

So this sentence means something like:

• Whenever the pet food runs out at home, I immediately go to the pet store after work.

This is not about one specific event. It is about a general routine.

That is why both verbs are in the present tense:

• заканчивается = runs out
• иду = go

If the speaker wanted to describe one specific future event, Russian would likely use a different structure.

Иду is the imperfective present form of идти, and here it expresses a habitual reaction:

• я сразу иду в зоомагазин = I go straight to the pet store

Russian often uses the present tense for repeated behavior.

If you said пойду, that would sound more like I will go in one specific future situation:

• Когда дома закончится корм, я сразу пойду в зоомагазин. = When the pet food runs out, I’ll go straight to the pet store.

So:

• иду = usual repeated action
• пойду = one specific future action

Because the sentence expresses motion toward a destination.

Russian uses:

• в + accusative for motion into/to
• в + prepositional for location in/at

So:

• иду в зоомагазин = I am going to the pet store
• я в зоомагазине = I am in/at the pet store

Here зоомагазин is masculine singular, so the accusative form is the same as the nominative:

• зоомагазин → в зоомагазин

После requires the genitive case.

So:

• после
  • genitive = after

The noun работа becomes работы in the genitive singular:

• работа → работы

So:

• после работы = after work

This is a very common expression in Russian.

Other examples:

• после урока = after the lesson
• после обеда = after lunch

Сразу means right away, immediately, or straight away.

In this sentence:

• я сразу иду в зоомагазин после работы

it means the speaker does not delay; going to the pet store is the immediate next step after work.

Its position is quite natural. Russian word order is flexible, but placement often shows emphasis.

Here сразу comes before иду:

• я сразу иду... = I immediately go...

You could move it around, but the nuance may shift slightly:

• Я иду сразу после работы... = more emphasis on right after work
• Я сразу после работы иду... = also emphasizes timing

The original sentence is perfectly natural.

It means after work, so the action happens once work is over.

The whole sentence means something like:

• Whenever we run out of pet food at home, I go to the pet store right after work.

So сразу does not mean at the exact moment the food runs out. It means the speaker goes as soon as reasonably possible in that routine — namely after work.

That is an important difference.

Russian often leaves possession or reference unstated when it is obvious from context.

So дома here simply means:

• at home
• in the household

Depending on context, English might translate it as:

• at home
• at our place
• at my house

Russian does not need to say у нас дома or у меня дома unless the speaker wants to be more specific.

Compare:

• Когда дома заканчивается корм... = neutral, natural
• Когда у нас дома заканчивается корм... = When we run out of pet food at home / at our place...

Both are possible.

It most naturally describes a repeated habit.

The clues are:

• когда in the sense of whenever
• present tense verbs: заканчивается, иду
• the overall structure of a routine or general rule

So the meaning is:

• Whenever the pet food runs out at home, I go to the pet store after work.

If the speaker wanted to describe one particular future event, Russian would more likely say:

• Когда дома закончится корм, я сразу пойду в зоомагазин после работы.

That would mean:

• When the pet food runs out, I’ll go to the pet store after work.

So the original sentence is best understood as a usual pattern.