Obre l'ordinador i mira el correu abans de la classe.

It is a command/instruction.

More specifically, obre and mira are affirmative imperative forms, used here to tell one person what to do in an informal way (tu).

• obre = open
• mira = look/check

So the sentence is giving a sequence of actions.

Catalan often omits subject pronouns when they are not needed.

In English, you usually need you:

• Open the computer and check the email

In Catalan, the verb form already makes the instruction clear, so tu is normally left out:

• Obre...
• Mira...

You could add tu for emphasis, but it is not necessary.

Because the masculine singular article el becomes l' before a vowel sound.

So:

• el + ordinador → l'ordinador

This apostrophe is very common in Catalan:

• l'escola
• l'amic
• l'hotel

It is the same article, just in a shortened form.

Yes, literally it means open the computer.

In context, that can make sense if you are talking about:

• opening a laptop
• opening/accessing a computer system
• opening something on the computer

If you specifically mean turn on the computer, Catalan often uses engega l'ordinador instead.

So obre is literally open, not automatically switch on.

Yes, mirar basically means to look at, but in everyday Catalan it can also mean check in contexts like email, messages, or information.

So:

• mira el correu can mean look at the mail/email
• in natural English, this is often translated as check your email

This is a normal, natural use of mirar.

correu can mean either mail/post or email, depending on context.

Here, because the sentence mentions l'ordinador, learners will usually understand el correu as email.

If you want to be completely explicit, Catalan can also say:

• correu electrònic = email

But in many everyday situations, just correu is enough.

Catalan often uses the definite article where English would use a possessive.

So:

• mira el correu can naturally mean check your email

The ownership is understood from the situation, so teu is often unnecessary.

You can say el teu correu, but it usually adds emphasis or contrast:

• Mira el teu correu, no el meu.

abans de means before when it is followed by:

• a noun
• an infinitive

Examples:

• abans de la classe = before class / before the class
• abans de sortir = before leaving

The de is part of the normal structure.

If a full clause follows, Catalan usually uses abans que instead:

• abans que comenci la classe = before class starts

Because la classe refers to a specific class/session.

So:

• abans de la classe = before the class / before class

Using the article here is normal and natural. Without the article, the phrase would sound less complete in this sentence.

Catalan often uses articles in places where English may or may not use one.

No. Here classe means class, lesson, or teaching session.

If you mean the physical room, aula is often the clearer word:

• classe = class / lesson
• aula = classroom

So in this sentence, abans de la classe means before the lesson starts, not before entering the room.

Here the sentence is informal singular (tu).

Other common versions are:

• Formal singular (vostè):
  Obri l'ordinador i miri el correu abans de la classe.

• Informal plural (vosaltres):
  Obriu l'ordinador i mireu el correu abans de la classe.

• Formal plural (vostès):
  Obrin l'ordinador i mirin el correu abans de la classe.

So the main thing that changes is the verb form.