Learn Hardcore Russian: Я хочу зайти в магазин вечером. - I want to stop by the store in the evening.

в + accusative = motion to / into a place
- в магазин – into the store (you are going there)
в + prepositional = location in a place
- в магазине – in the store (you are already there)

In Я хочу зайти в магазин вечером, the verb зайти expresses movement into the store, so Russian uses в + accusative → в магазин.

What exactly does зайти mean here, compared with идти or пойти?

All three are motion verbs, but with different nuances:

идти (в магазин) – to go (on foot) to the store
Neutral “go”, no detail about how long you’ll stay.
пойти (в магазин) – to set off / start going to the store
Focus on the beginning of the movement.
зайти (в магазин) – to pop into / drop by / stop in the store
- Has the prefix за-, suggesting a short visit, going in briefly.
- Implies you’ll enter, do something quickly (buy something), and then leave.

So Я хочу зайти в магазин вечером very naturally means:
“I want to pop into the store in the evening (for a short visit).”

Why is зайти (perfective) used after хочу? Could I say Я хочу заходить в магазин вечером?

In Russian, after verbs like хотеть (to want), you usually choose:

Perfective infinitive for one complete future action or a specific instance:
- Я хочу зайти в магазин вечером.
  → I want to (at some point this evening) go in once and be done.
Imperfective infinitive for repeated / habitual / ongoing actions:
- Я хочу заходить в магазин вечером.
  This sounds like: “I want to make it a habit to drop by the store in the evenings.”
  (e.g., as a new routine.)

So Я хочу зайти в магазин вечером is about one planned visit this evening, which is why зайти (perfective) is normal here.

Why is it вечером and not вечер or в вечером?

Вечером is the instrumental case of вечер (evening) and is commonly used to say “in the evening” (time when):

утром – in the morning
днём – in the daytime
вечером – in the evening
ночью – at night

You do not say в вечером in standard Russian.

Alternatives:

сегодня вечером – this evening
завтра вечером – tomorrow evening

But used alone, вечером = in the evening (later today) in most contexts.

Can I change the word order? For example: Вечером я хочу зайти в магазин or Я вечером хочу зайти в магазин?

Yes, Russian word order is flexible, and all of these are grammatical:

Я хочу зайти в магазин вечером.
Neutral, common. Slightly emphasizes what you want (to go to the store) and then when.
Вечером я хочу зайти в магазин.
Emphasizes “in the evening” (as opposed to some other time). Good if you contrast times:
- Утром я занят, а вечером я хочу зайти в магазин.
Я вечером хочу зайти в магазин.
Slightly emphasizes вечером too, but keeps я at the start. Very natural in speech.

Meaning stays essentially the same; only nuance of emphasis changes.

Why is it я хочу, not something like я хотю? How does хотеть conjugate?

Хотеть is irregular; you must memorize its forms. For the singular:

я хочу – I want
ты хочешь – you (sg.) want
он / она / оно хочет – he / she / it wants

There is no form хотю in standard Russian. The stress is:

я хочу́ (stress on -у́)
ты хо́чешь
он/она хо́чет

So я хочу зайти… is simply the correct 1st person singular form of хотеть.

Why is зайти in the infinitive form after хочу? Could I say Я хочу захожу?

In Russian, after verbs expressing desire/ability/necessity (like хотеть, мочь, любить, нужно), you use an infinitive, not a conjugated verb:

Я хочу зайти… – I want to go in…
Я могу зайти… – I can go in…
Мне нужно зайти… – I need to go in…

So Я хочу захожу is wrong, just like “I want I go” is wrong in English.
It must be Я хочу зайти (I want to go in).

Can I drop the pronoun я and just say Хочу зайти в магазин вечером?

Yes, you can. In Russian, subject pronouns are often omitted when the verb form already shows the person:

Хочу зайти в магазин вечером.
→ Still clearly means “I want to pop into the store in the evening.”

Nuance:

With я: Я хочу зайти… – slightly more explicit, can sound a bit more emphatic or formal.
Without я: Хочу зайти… – common in conversation, messages, notes; sounds more casual.

Both are correct and natural.

Is магазин in the accusative case here? It looks the same as the nominative.

Yes, магазин is in the accusative because it’s the destination of motion after в:

Куда? (Where to?) – в магазин → accusative
Где? (Where?) – в магазине → prepositional

For masculine inanimate nouns like магазин, the nominative and accusative forms are identical:

Nominative: магазин – the store (subject)
Accusative: в магазин – to the store

You recognize the case not by the form, but by the combination в + куда? (motion → accusative).

Could I say Я хочу пойти в магазин вечером instead? How is that different from зайти?

Yes, you can, but the nuance changes:

Я хочу зайти в магазин вечером.
→ I want to pop into the store in the evening (short stop, go in and out).
Я хочу пойти в магазин вечером.
→ I want to go to the store in the evening (neutral; no special focus on it being brief or “on the way”).

Both are correct; зайти feels more like “drop by quickly (maybe on my way somewhere)”, while пойти is just “go (there)” without that “quick visit” flavor.