"This is my hat."
Translation:Це моя шапка.
Де means where, це means this. Since Ukrainian doesn't usually include the verb to be in the present tense, they can be used to mean this is (these are) and where is/are.
шапка is accepted, but your answer had a typo. You entered "мій" instead of "моя." Please, check your answers before reporting.
I could swear the highlighted word was капелюх.... I apologize anyways. Thanks for the quick reply!