"I buy three oranges."
Translation:Jag köper tre stycken apelsiner.
Yes, three individual oranges in this case. We like to use this expression when talking about things that are counted. Especially at the end of sentences, like this: - Hur många böcker köpte du? - Tre stycken. 'How many books did you buy? - Three.'
PS revisited this comment 8 months later and want to add this: I'm not sure if stycken is technically the plural of ett stycke. At least in my speech, the plural of stycke has a different tonal accent than this word. (the one meaning 'ones' has the acute accent.)
Would omitting stycken in these contexts be wrong, or is it just less common?
It works fine without it too, especially in a sentence like this. It's more that we wanted to teach you this word since it's pretty common.
Ok but "pieces/stycken" was not contemplated in the English sentence, so, I think, you cannot consider wrong not having checked that choice. :)
I think 'att handla' is more like 'to shop', for food not for clothes. Still I shop three oranges is really weird in English as well, so I am assuming it is not correct.