Он не курит.

Он means he.

You use он for a male person or for a masculine noun that has already been mentioned. In this sentence, it is simply the subject: he.

Russian also has:

• она = she
• оно = it
• они = they

Не is the basic word for not in Russian.

To make a sentence negative, you usually put не directly before the word you are negating. In Он не курит, it comes before the verb, so the whole idea is he does not smoke.

Compare:

• Он курит. = He smokes.
• Он не курит. = He does not smoke.

Курить is the dictionary form, meaning to smoke.

In the sentence, you need a finite verb that matches the subject. Since the subject is он (he), Russian uses the 3rd person singular present-tense form:

• курить = to smoke
• он курит = he smokes

So курит is the correct conjugated form for he.

Because Russian verb endings show the person and number.

For курить, the present tense goes like this:

• я курю = I smoke
• ты куришь = you smoke
• он / она / оно курит = he / she / it smokes
• мы курим = we smoke
• вы курите = you smoke / you all smoke
• они курят = they smoke

So the ending -ит tells you it is 3rd person singular.

Russian does not use a separate auxiliary verb like do / does in the present tense.

English says:

• He smokes
• He does not smoke

Russian just uses the main verb:

• Он курит
• Он не курит

So не does the negating, and the verb form itself already tells you the subject.

Sometimes, yes.

Russian often drops subject pronouns when the meaning is clear from context, because the verb ending already gives information. So in conversation, Не курит can mean He doesn’t smoke, if it is already obvious who you mean.

Still, Он не курит is a perfectly normal full sentence and is often the best form for learners to use.

The most neutral word order is:

• Он не курит.

Russian word order is more flexible than English, but changing it changes the emphasis.

For example:

• Он не курит. = neutral statement
• Не курит он. = marked/emphatic, something like It’s he who doesn’t smoke or He doesn’t smoke, actually
• Курит он? = more like Does he smoke? with a particular emphasis

So for normal use, stick with Он не курит.

The stress is on the first syllable of курит:

• он не ку́рит

A rough pronunciation guide:

• он ≈ on
• не is usually pronounced more like nye or short ni
• ку́рит ≈ KOO-rit, with a softer r and t than in English

In IPA, it is approximately:

• [on nʲɪ ˈkurʲɪt]

The important stress point is:

• ку́рит, not кури́т

Most naturally, Он не курит means he doesn’t smoke in a general or habitual sense.

Russian present-tense imperfective verbs often describe:

• habits
• repeated actions
• general facts
• what is happening now, depending on context

So this sentence can sometimes mean he isn’t smoking in a particular situation, but without extra context, learners should usually understand it as the general statement he doesn’t smoke.

If you want to make right now clearer, you can say:

• Он сейчас не курит. = He isn’t smoking right now.

Russian has no articles.

So Russian does not have separate words corresponding to a, an, or the. That is why the sentence is simply:

• Он не курит.

You do not need to add anything for the or a.

Курить is an imperfective verb.

That matters because in Russian:

• imperfective verbs have present-tense forms
• perfective verbs do not have a true present tense; their “present” forms usually refer to the future

Since this sentence is about a present/general action, курить is exactly what you want.

Very roughly:

• курить = to smoke, be a smoker, smoke habitually
• a perfective verb like закурить often means something more like to start smoking / light up

So Он не курит is the normal way to say He doesn’t smoke.

In Russian, yes/no questions are often made just by intonation.

So you can say:

• Он не курит? = Does he not smoke? / He doesn’t smoke?

The word order can stay the same. Your voice rises to show that it is a question.

You can also ask:

• Он курит? = Does he smoke?

Usually, yes, when the whole action is being negated.

So:

• Он не курит. = He does not smoke.

That is the standard pattern. But if you are negating some other part of the sentence, не may go before that other word instead.

For example:

• Он курит не дома. = He smokes not at home.
• Не он курит. = It is not he who smokes.

In your sentence, the action itself is negative, so не goes before the verb.

Yes: не is written separately from the verb.

With verbs, не is normally written as a separate word:

• не курит
• не знает
• не говорит

This is an important spelling rule for beginners. There are some special exceptions in Russian, but as a basic rule, with verbs you should write не separately.