This sounds really dumb, but how do あなた like a picture または video? I have been trying to figure this out for a while. Thank you!!

あなた can be a ファン of It. Unless あなた uploaded the image yourself, then あなた already are a ファン of it. And あなた can save it to your favorites.

あなた click the "Fan of it" button which is on the right beneath the image または video.