Infla la cambra d'aire.

Here it is most naturally understood as a command: Inflate the inner tube.

That is because infla can be:

• the tu imperative of inflar = inflate!
• also the 3rd person singular present = he/she/it inflates

In isolation, the form is ambiguous, but in a short instruction like Infla la cambra d'aire., it is read as an imperative.

Catalan often omits subject pronouns when they are not needed.

So instead of saying:

• Tu infla la cambra d'aire

Catalan normally just says:

• Infla la cambra d'aire

This is especially common in commands, where the subject is usually understood automatically.

Because cambra is a feminine singular noun, so it takes the feminine singular article la.

• la cambra
• not el cambra

Catalan articles have to agree with the noun in gender and number.

Literally, cambra d'aire means air chamber.

In everyday use, it commonly refers to an inner tube, especially the inflatable tube inside a tire.

So even if the literal wording is air chamber, the natural meaning in context is often inner tube.

This is because de becomes d' before a word beginning with a vowel.

So:

• de + aire → d'aire

This is a very common feature in Catalan, called elision.

You will see the same kind of thing in many other words and phrases, such as:

• l'amic
• d'aigua
• m'agrada

Because in this expression, aire is being used in a general, descriptive sense, not as the air.

So cambra d'aire means something like:

• a chamber made for / filled with air
• not a chamber of the air

Catalan often uses noun + de + noun without an article in this kind of fixed expression.

A simple learner-friendly pronunciation guide is:

EEN-fluh luh KAHM-bruh DAI-ruh

A few notes:

• infla: stress on the first syllable
• cambra: stress on cam-
• aire: pronounced roughly like AI-re

In many eastern varieties of Catalan, the unstressed a sounds more like a soft uh sound.

The form changes depending on who you are speaking to:

• Infla la cambra d'aire. = informal singular (you, one person)
• Infli la cambra d'aire. = formal singular
• Infleu la cambra d'aire. = plural informal
• Inflin la cambra d'aire. = formal plural

So the sentence you were given is the informal singular command.

Yes. If the object is already known, Catalan can replace it with a direct object pronoun.

So:

• Infla la cambra d'aire. = Inflate the inner tube.
• Infla-la. = Inflate it.

In affirmative commands, the pronoun is usually attached to the verb with a hyphen:

• infla-la
• porta'l
• fes-ho

That is a very common Catalan pattern.