Перш ніж натиснути кнопку, подивися на екран.

Перш ніж is a fixed conjunction meaning before. It introduces a subordinate clause.

So in Перш ніж натиснути кнопку, подивися на екран, the перш ніж part sets up the earlier requirement, and the main clause gives the instruction.

A natural way to think of it is:

Before pressing the button, look at the screen.

It is best learned as one unit: перш ніж.

The comma separates the subordinate clause from the main clause.

• Перш ніж натиснути кнопку = subordinate clause
• подивися на екран = main clause

Ukrainian normally uses a comma here, just as English often does in sentences like Before you press the button, look at the screen.

After перш ніж, Ukrainian often uses the infinitive when the subject is understood and is the same person as in the main clause.

So:

• Перш ніж натиснути кнопку, подивися на екран
  means
• Before pressing the button, look at the screen

The person who will look is also the person who will press, so Ukrainian can leave that unstated and use the infinitive.

Yes. That is also correct:

Перш ніж ти натиснеш кнопку, подивися на екран.

This version is more explicit because it includes ти and a finite verb form натиснеш.

The infinitive version sounds compact and very natural in instructions. The full-clause version may sound slightly more explicit or emphatic.

This is about aspect.

• натиснути = perfective, a single completed press
• натискати = imperfective, repeated action, ongoing action, or general process

Here the sentence refers to one specific action: pressing the button once. That is why натиснути is the natural choice.

If you used натискати, it would suggest something more like pressing repeatedly or the act/process of pressing, which does not fit as well here.

Again, this is mainly aspect and nuance.

• подивися = take a look, have a look
• дивись = look, watch, sometimes keep looking, or even watch out

In this sentence, the speaker wants one quick, complete action before something else happens: take a look at the screen. That makes подивися a very good choice.

So:

• подивися на екран = take a look at the screen
• дивись на екран = look at the screen / keep looking at the screen

-ся is the reflexive marker, but in many verbs it is simply part of the verb and does not translate as a literal English reflexive.

Here the base verb is подивитися. Its imperative singular is подивися.

So you should learn подивитися на щось as a whole pattern meaning:

to look at something / to take a look at something

In other words, -ся is not something you should try to translate word-for-word here. It is just part of the verb form.

Because the imperative verb already tells you that the instruction is addressed to you singular.

• подивися = look / take a look addressed to one person

Ukrainian often omits subject pronouns when they are already clear from the verb form. Adding ти is possible, but it usually adds emphasis:

...ти подивися... would sound more marked or emphatic.

Because кнопку is the accusative singular form of кнопка.

The verb натиснути takes a direct object, and direct objects are commonly in the accusative case.

So:

• nominative: кнопка
• accusative singular: кнопку

This is the normal pattern for a feminine noun in -а.

Because after дивитися / подивитися на, Ukrainian uses на + accusative to mean look at something.

So:

• подивися на екран = look at the screen

But:

• на екрані = on the screen

That second form is about location, not the object of looking. For example:

• На екрані є помилка = There is an error on the screen

So in your sentence, екран is in the accusative: екран.

Yes. Ukrainian word order is flexible.

You can also say:

Подивися на екран, перш ніж натиснути кнопку.

The meaning stays the same. The difference is mostly emphasis:

• Перш ніж... first = foregrounds the condition or sequence
• Подивися... first = foregrounds the command itself

Both are natural.

You would use the plural/polite imperative:

Перш ніж натиснути кнопку, подивіться на екран.

• подивися = singular informal
• подивіться = plural or polite singular

This is very common in instructions, announcements, and formal speech.

Yes, very much so.

The pattern

Перш ніж + infinitive, imperative

is common in instructions, manuals, warnings, and interface text. It sounds natural, concise, and clear.

You will often see similar structures such as:

• Перш ніж почати, прочитайте інструкцію.
• Перш ніж увійти, перевірте дані.

So this sentence is a very useful model to remember.