Он пьян, поэтому не может водить.

In Russian, the verb to be is usually omitted in the present tense.

So:

• Он пьян = He is drunk
• literally: He drunk

This is completely normal in Russian. You do the same with many sentences:

• Он дома = He is at home
• Она счастлива = She is happy

If you want past or future, then forms of быть appear:

• Он был пьян = He was drunk
• Он будет пьян = He will be drunk

Пьян is the short form of the adjective пьяный.

In Russian, short-form adjectives are often used:

• in the predicate
• for temporary states
• especially in set expressions like being drunk, ready, glad, etc.

So:

• Он пьян = He is drunk
• Он пьяный also exists, but it can sound a little more descriptive or colloquial, as if you are describing him as a drunk person / a drunk-looking man in that moment.

In this sentence, пьян is the most standard and natural choice.

Yes, пьян is the masculine singular form, so it matches он.

Other forms are:

• она пьяна = she is drunk
• оно пьяно = it is drunk
• они пьяны = they are drunk

Russian adjectives must agree with the noun or pronoun in gender and number.

Поэтому means therefore, so, that’s why, or for that reason.

In this sentence:

• Он пьян, поэтому не может водить.
• He is drunk, so he cannot drive.

It connects the two ideas in a cause-and-result way:

• cause: Он пьян
• result: не может водить

It is a very common linking word in Russian.

Because the sentence contains two linked parts:

• Он пьян
• поэтому не может водить

In standard Russian punctuation, a comma is normally used before поэтому when it connects clauses like this.

So the comma helps show the pause and logical relationship:

• He is drunk, therefore he cannot drive.

Russian often omits a repeated subject when it is already clear from context.

So:

• Он пьян, поэтому не может водить.

means the same as the more explicit:

• Он пьян, поэтому он не может водить.

The second он is unnecessary because the subject is obvious. Omitting it sounds natural and avoids repetition.

Не может means cannot or is not able to.

It comes from the verb мочь = to be able / can.

Here:

• может = can
• не может = cannot

In this sentence, it means he is unable to drive because he is drunk.

Depending on context, не может can sometimes mean:

• physically cannot
• is not allowed to
• is not capable of

But here the meaning is clearly he can’t drive because he’s drunk.

Because водить here means to drive a vehicle.

Compare:

• водить машину = to drive a car
• ехать = to go / be going by transport in one specific trip
• ездить = to go by transport regularly / repeatedly

So:

• Я не умею водить. = I don’t know how to drive.
• Я еду домой. = I’m going home.
• Я часто езжу на автобусе. = I often go by bus.

In your sentence, the point is not that he is traveling somewhere, but that he is driving a vehicle, so водить is the correct verb.

Because the object can be omitted when it is obvious.

• водить машину = to drive a car
• водить by itself can mean to drive in a general sense

So:

• Он не может водить = He can’t drive
• Он не может водить машину = He can’t drive a car

The shorter version sounds natural when the listener already understands that driving a vehicle is meant.

Yes. Водить has several meanings depending on context.

It can mean:

• to drive a car or vehicle
• to lead / guide
• to take someone somewhere regularly

For example:

• водить машину = to drive a car
• водить туристов по музею = to guide tourists through a museum
• водить детей в школу = to take children to school

In your sentence, because of the context, водить clearly means drive.

Yes, Russian word order is fairly flexible.

These are all possible, though the emphasis changes a little:

• Он пьян, поэтому не может водить.
• Он пьян, поэтому он не может водить.
• Поэтому он не может водить.
  if the reason was already mentioned before
• Он не может водить, потому что пьян.

The version you have is very natural and neutral.

This is a very common question.

• поэтому = therefore / so / that’s why
• потому что = because

Compare:

• Он пьян, поэтому не может водить.
  He is drunk, so he can’t drive.

• Он не может водить, потому что пьян.
  He can’t drive because he is drunk.

They express the same basic idea, but the structure is reversed:

• cause → result with поэтому
• result → cause with потому что

The stress is on the last syllable:

• води́ть

Approximate pronunciation: va-DEET’

A few useful stress points in the sentence are:

• Он пьян
• поэ́тому
• не мо́жет
• води́ть

Stress matters in Russian, so it is good to learn words together with their stress.

Yes, it is natural and correct.

A native speaker might also say:

• Он пьян, поэтому ему нельзя водить.
  = He is drunk, so he mustn’t drive / he’s not allowed to drive.

• Он пьян, поэтому не может вести машину.
  = He is drunk, so he can’t drive the car.

• Он не может водить, потому что пьян.

But your original sentence is perfectly normal and idiomatic:

• Он пьян, поэтому не может водить.