N’appuie pas sur cette touche : elle ferme tous les onglets d’un seul coup.

Yes. N’appuie pas is the negative imperative of appuyer for tu.

• appuyer = to press
• appuie ! = press!
• n’appuie pas ! = don’t press!

French makes negative commands by putting ne ... pas around the verb:

• Ne parle pas. = Don’t speak.
• N’ouvre pas la porte. = Don’t open the door.
• N’appuie pas sur cette touche. = Don’t press this key/button.

Here, ne becomes n’ because the next word starts with a vowel sound: appuie.

Because this is the tu imperative form of an -er verb.

For most regular -er verbs, the tu imperative drops the final -s:

• tu appuies = you press
• appuie ! = press!

So:

• Tu appuies sur cette touche. = You press this key.
• Appuie sur cette touche. = Press this key.
• N’appuie pas sur cette touche. = Don’t press this key.

A learner might expect appuies because that is the normal tu present form, but commands usually use the special imperative form without the subject pronoun and without that final -s.

Because in the imperative, French normally leaves out the subject pronoun.

So instead of saying:

• Tu n’appuies pas sur cette touche

you say:

• N’appuie pas sur cette touche

That is one of the clearest signs that this is a command or instruction rather than a normal statement.

Because appuyer often takes the preposition sur when it means to press on something.

So:

• appuyer sur un bouton = to press a button
• appuyer sur une touche = to press a key
• appuyer sur l’écran = to press on the screen

English often says simply press the button, but French usually uses appuyer sur.

Here touche means a key or button, depending on context.

Common uses:

• on a keyboard: une touche = a key
• on a device or control panel: une touche = a button

So in this sentence, it could mean:

• a keyboard key
• a shortcut key
• a button in some interface

It does not mean the English noun touch here.

Because touche is a feminine singular noun.

French demonstratives must agree with the noun:

• ce = this/that for masculine singular
• cette = this/that for feminine singular
• ces = these/those for plural

So:

• ce bouton = this button
• cette touche = this key/button
• ces touches = these keys/buttons

Elle refers to cette touche.

Since touche is feminine, the pronoun that refers back to it is elle:

• cette touche → elle

So the sentence structure is:

• N’appuie pas sur cette touche = Don’t press this key
• elle ferme tous les onglets d’un seul coup = it closes all the tabs at once

In English, we usually say it for an object, but in French nouns have grammatical gender, so a feminine noun can be referred to as elle.

Because French often uses the present tense to describe what something does or what its normal effect is.

So:

• elle ferme tous les onglets literally means it closes all the tabs

This is natural in French when describing:

• a function
• a habit
• a general result
• an instruction-related consequence

It is similar to English sentences like:

• This button opens the menu.
• This key deletes the file.

So the present tense here means that is what this key does.

Because tous les onglets means all the tabs—the whole set of tabs being talked about.

• des onglets = some tabs / tabs
• les onglets = the tabs
• tous les onglets = all the tabs

The sentence is warning that pressing this key closes every tab currently open, not just some of them.

Also note:

• tout le monde = everyone
• toute la journée = the whole day
• tous les onglets = all the tabs

Un onglet usually means a tab, especially in computing.

Examples:

• un onglet du navigateur = a browser tab
• ouvrir un nouvel onglet = open a new tab
• fermer un onglet = close a tab

Outside computing, onglet can have other meanings in specialized contexts, but for most learners here, the important meaning is tab.

D’un seul coup is an idiomatic expression meaning:

• in one go
• all at once
• in a single stroke
• suddenly, depending on context

In this sentence, it means the tabs are all closed at the same time, not one by one.

Examples:

• Il a tout mangé d’un seul coup. = He ate everything in one go.
• La porte s’est ouverte d’un seul coup. = The door opened all at once / suddenly.
• Elle ferme tous les onglets d’un seul coup. = It closes all the tabs at once.

The colon introduces an explanation or reason for the warning.

So the structure is:

• Don’t press this key:
• it closes all the tabs at once.

The second part explains why you should not press it.

French uses the colon much like English does in this kind of sentence.

You would use the vous imperative:

• N’appuyez pas sur cette touche : elle ferme tous les onglets d’un seul coup.

Compare:

• N’appuie pas ... = don’t press ... (to one person, informal)
• N’appuyez pas ... = don’t press ... (to several people, or one person formally)

That is a very common distinction in French.