Learn French: Nous avons loué l'hélicoptère il y a une heure. Celui-ci est très rapide. - We rented the helicopter an hour ago. This one is very fast.

Celui-ci translates to "this one". We use it to point out the specific helicopter we just mentioned. It is made of celui (the masculine singular pronoun, matching hélicoptère) and the suffix -ci (meaning "this" or "here"). While il just means "it", celui-ci puts special emphasis on "this specific one".

If I were talking about a car (la voiture) instead of a helicopter, would I still use celui-ci?

No, you would use celle-ci. Demonstrative pronouns must match the gender of the noun they replace. Since voiture is feminine, you use the feminine form celle plus the -ci suffix. We use celui-ci here because hélicoptère is masculine.

Doesn't il y a mean "there is"? Why does it mean "ago" in this sentence?

You are right that il y a usually means "there is" or "there are". However, when it is placed before a period of time, like une heure (an hour), it changes meaning to "ago". Therefore, il y a une heure means "an hour ago".

Why is it avons loué instead of just louons?