Сядь дальше от окна, если от форточки идёт сквозняк.

Сядь is the singular informal imperative of сесть, the perfective verb meaning to sit down / take a seat.

• сесть → сядь = tell one person informally to sit down
• сесть → сядьте = tell several people, or one person politely/formally

The perfective form fits because this is a one-time action: change your position and end up sitting farther from the window.

This is a very common question, because both can be translated as sit down.

• сядь is perfective: it focuses on the result of a single action.
• садись is imperfective: it sounds more process-oriented, repeated, or gently invitational depending on context.

In this sentence, the speaker wants one concrete action: move and sit farther away. That is why сядь works well.

A useful nuance:

• If the person is already sitting and you want to emphasize changing seats, Russian often uses пересядь:
  Пересядь дальше от окна.

Russian usually omits the subject pronoun in commands because the verb form already shows who the command is addressed to.

So сядь already means something like you sit down addressed to one person informally.

You would only add ты or вы for special emphasis, contrast, or emotion:

• Ты сядь дальше от окна.
• Вы сядьте дальше от окна.

Most of the time, the pronoun is unnecessary.

Yes. Дальше is the comparative adverb of далеко.

Here it means farther away:

• Сядь дальше от окна = sit farther from the window

It does not mean continue here. It is purely about distance.

A related word you may also hear is подальше:

• Сядь подальше от окна

That is also very natural, and in everyday speech it can sound even a little more idiomatic for move farther away.

Very roughly:

• дальше = farther
• подальше = a bit farther away / farther off

Because both follow the preposition от, and от takes the genitive case when it means from or away from.

So:

• окно → от окна
• форточка → от форточки

This is the normal pattern:

• от дома = from the house
• от двери = from the door
• от окна = from the window

In this sentence, от shows source or distance away from something.

Форточка is a small vent window or small opening pane in a window, traditionally used for ventilation.

It is not usually the whole window. It is a small part of the window that can be opened to let air in.

This is a very culturally common household word in Russian, especially with older-style windows. So:

• окно = window
• форточка = small vent window / little window flap

Yes, literally it is something like a draft is going / coming.

That sounds odd in English, but it is a normal Russian way to describe moving air or an ongoing natural phenomenon. Russian often uses идти in expressions like this.

So идёт сквозняк is idiomatic Russian for there is a draft or a draft is coming through.

Other natural ways to say something similar are:

• Из форточки дует. = It is blowing from the vent window.
• От форточки тянет. = A draft is coming from the vent window.
• Сквозит. = There is a draft.

So the wording in the sentence is normal, even if the literal English sounds unusual.

Because если introduces a subordinate clause, and Russian normally separates subordinate clauses with a comma.

So the structure is:

• main clause: Сядь дальше от окна
• subordinate conditional clause: если от форточки идёт сквозняк

That is why there is a comma: Сядь дальше от окна, если от форточки идёт сквозняк.

You can also reverse the order: Если от форточки идёт сквозняк, сядь дальше от окна.

Both are correct.

That is not strange.

The sentence is doing two slightly different things:

• от форточки names the specific source of the draft
• от окна gives the practical area to move away from

Since форточка is part of the window, the advice is broader: move away from the window area.

So the logic is:

• if the draft is coming from the vent window,
• sit farther from the window

If you wanted to make both parts match more exactly, you could say:

• Сядь дальше от форточки, если от неё идёт сквозняк.

But the original version sounds natural.

Yes, the sentence is informal because of сядь.

To say it politely to one person, or to several people, use сядьте:

Сядьте дальше от окна, если от форточки идёт сквозняк.

So:

• сядь = informal singular
• сядьте = polite singular or plural

This is a very important imperative pattern in Russian.