Learn French: Le laboratoire est libre. Nous y allons pour préparer notre exposé. - The laboratory is free. We are going there to prepare our presentation.

y is an adverbial pronoun that means "there". It replaces a location that was just mentioned—in this case, the laboratory (le laboratoire). In French, pronouns like y almost always go immediately before the conjugated verb, which is why we say Nous y allons instead of saying Nous allons y.

Does libre mean "free of charge" here?

No, in this context libre means "available" or "unoccupied". If you wanted to say something is free of charge because it costs no money, you would use the word gratuit.

Why do we use pour préparer instead of just préparer?

In French, when you want to say "in order to do something", you use the preposition pour followed by an infinitive verb (the basic, unconjugated form). So, pour préparer translates perfectly to "in order to prepare".

The word exposé looks like the English word "expose". Does it mean the same thing?

Not quite! While their origins are related, in a school or academic context, an exposé is an oral presentation or a report. It is a very common everyday term for a class presentation.