Learn Swedish: Vi köper biljetter på stationen. - We buy tickets at the station.

The singular word is en biljett (a ticket). It belongs to a group of nouns (Group 3) that form their plural by adding -er. Many of these are loanwords from other languages with the stress on the last syllable.

Why do we use på for "at the station"?

In Swedish, you typically use på (which often translates to "on") for public buildings, services, or institutions. Just like you say på banken (at the bank), you say på stationen (at the station).

What does the -en at the end of stationen do?

It makes the noun definite, meaning "the station". Instead of putting a separate word for "the" in front of the noun like English does, Swedish attaches -en to the end of singular "en"-words like en station.

Does Vi köper mean "We buy" or "We are buying"?

It means both! Swedish does not have a separate continuous tense. Vi köper covers both a general habit and an action happening right now.