"They buy clothes in June."

Translation: W czerwcu oni kupują ubrania.

[lstrzelak]

Why isn't 'ciuchy' correct?

[mihxal]

"Ubrania" is a standard word. But you're right "ciuchy" is a quite common colloquial word.

[NickFleck]

I wrote one instead oni. How was I to know gender?

[moza1642]

Can't we omit "oni" (they) in the polish sentence?

[immery]

You can always omit "oni/one" in polish sentence. It is less common than omitting ja/ty/my/wy.

[MsenRezaee]

Is it correct to say "Oni kupują ubrania w czerwcu"?

[Jellei]

Yes, perfectly correct and accepted.