"The man is wearing a hat."
Translation:Der Mann trägt einen Hut.
Hi, I studied German ay A Level so I can help you out here! Because "Hut" is now the object of the sentence so it is in the acusative case. The masculine article is "ein" when something is the subject of a sentence and therefore in the nominative case and "einen" when it is the object and therefore in the acusative case :)