Learn Portuguese (Portugal): Vamos àquela bilheteira comprar os bilhetes para a montanha-russa. - Let's go to that ticket office to buy the tickets for the roller coaster.

The verb ir (here used as vamos, meaning "let's go") requires the preposition a ("to") when talking about going to a destination. We are going to "that ticket office", which is aquela bilheteira. When the preposition a meets the demonstrative aquela, they merge into àquela. The grave accent tells you the preposition is hidden inside!

Why is the verb comprar left in its dictionary form?

Because it expresses the purpose of the trip. When you go somewhere to do an action, the second verb stays in the infinitive (the unconjugated dictionary form). Here, vamos... comprar translates directly to "let's go... to buy" without needing an extra word for "to".

What is the connection between bilheteira and bilhetes?

A bilhete is a "ticket". The ending -eira is often used in Portuguese to indicate a place or container associated with a noun. Therefore, a bilheteira is the ticket office or box office where the bilhetes are sold.

Why is a roller coaster called a montanha-russa?

Literally, it means "Russian mountain". This is a fun historical term used in Portuguese (and several other languages) because the earliest ancestors of roller coasters were actually steep ice sledding hills built in Russia during the 18th century!