У аварийного выхода висит инструкция, как действовать во время пожара.

Yes. In this sentence, у means something like by / near / next to.

• у аварийного выхода = by the emergency exit
• Literally, у normally means at the side of / near

Russian often uses у + genitive to say that something is located near something else.

So:

• У аварийного выхода висит инструкция = There is an instruction posted by the emergency exit

English often uses there is here, but Russian simply states the location first and then the thing that is there.

Because the preposition у requires the genitive case.

The basic dictionary form is:

• аварийный выход = emergency exit

But after у, both words change to genitive singular:

• аварийный → аварийного
• выход → выхода

So:

• у аварийного выхода = near the emergency exit

This is a very common pattern:

• у дома = near the house
• у двери = by the door
• у окна = by the window

Russian usually does not use a present-tense verb meaning is in ordinary sentences like this. Instead, it often uses a more specific verb.

Here, висит means is hanging.

So the sentence is literally something like:

• By the emergency exit hangs an instruction...

In natural English, we would usually say:

• There is an instruction posted by the emergency exit

Russian prefers the concrete verb висеть when something is physically hanging on a wall, door, etc.

Because инструкция is the subject of the sentence, so it is in the nominative case.

Even though it comes after the verb, it is still the thing doing the action of hanging:

• инструкция висит = the instruction is hanging

Russian word order is flexible, so the subject does not have to come first.

Compare:

• Инструкция висит у аварийного выхода.
• У аварийного выхода висит инструкция.

Both are grammatical. The second version sounds more natural if you first want to say where it is.

Because как действовать во время пожара is a subordinate clause attached to инструкция.

It explains the content of the instruction:

• инструкция, как действовать... = instructions on how to act...

Russian normally separates this kind of clause with a comma.

You can think of it as similar to English:

• an instruction on how to act during a fire

Russian uses the comma where English often would not.

It means how to act or what to do.

Breakdown:

• как = how
• действовать = to act / to proceed / to behave

So:

• инструкция, как действовать = instructions on how to act
• or more naturally, instructions on what to do

In emergency or official language, действовать is very common. It sounds a bit formal and procedural.

Because after как in this kind of structure, Russian often uses the infinitive to express a general instruction or method.

So:

• как действовать = how to act
• как пройти = how to get through
• как открыть = how to open

This is similar to English how to...

It is not tied to a specific person like how you should act; it is a general instruction.

Russian uses во instead of в before some word combinations for easier pronunciation.

Here:

• во время is the normal fixed expression meaning during

So:

• во время пожара = during a fire

You should learn во время as a set phrase.

Also, пожара is in the genitive case because во время requires genitive:

• пожар → пожара

Because the expression во время always takes the genitive.

Examples:

• во время урока = during the lesson
• во время встречи = during the meeting
• во время пожара = during the fire

So:

• пожар = fire
• пожара = of the fire / during the fire

This is just the case pattern required by the prepositional phrase.

Yes. Russian word order is flexible, although some versions sound more natural than others depending on emphasis.

For example:

• У аварийного выхода висит инструкция, как действовать во время пожара.
• Инструкция, как действовать во время пожара, висит у аварийного выхода.

Both are correct.

The original sentence starts with the location, which makes sense if the speaker wants to tell you where the instruction is.

Russian often puts known or setting information first, then introduces the main item after it.

Yes, in this context it is the normal translation.

• аварийный = emergency / emergency-related
• выход = exit

So аварийный выход is the standard phrase for emergency exit.

It is the usual wording you would expect on signs, in buildings, and in safety instructions.

It is normal standard Russian, but the vocabulary is a bit official / practical, because it is about safety instructions.

Words like these are common in signs and public notices:

• аварийный выход = emergency exit
• инструкция = instruction / instructions
• действовать = act / proceed
• во время пожара = during a fire

So it sounds very natural in a public building, workplace, school, or office.