Learn Portuguese (Portugal): Perdes o comboio ou o autocarro?

ou translates to 'or'. It is the conjunction we use to give a choice between two things, like the train or the bus. It is invariable, meaning it always stays as ou and never changes to match masculine, feminine, singular, or plural words.

I thought the verb perder meant 'to lose'. Why does it mean 'miss' here?

You are correct that perder usually means 'to lose' (like losing an item). However, in Portuguese, perder is also the exact verb you use when you 'miss' a form of transportation, like a train (comboio) or bus (autocarro).

Where are the words for 'Do you' in this sentence?

In Portuguese, you do not need helper verbs like 'do' to ask a question. The verb perdes is the 'tu' (informal you) form, so it already means 'you miss'. To turn it into a question, you simply write a question mark at the end and raise the pitch of your voice when speaking.

Do I have to repeat the word o before autocarro? Could I just say o comboio ou autocarro?

In English, it is normal to say 'the train or bus', dropping the second 'the'. In Portuguese, however, it is much better and more natural to keep the definite article before each noun in the choice: o comboio ou o autocarro.