Characterization

When i read the book, my teacher let me find the examples of characterization. But i am not sure if the Speech, thoughts, dress, behaviour, posture, physiognomy, hairstyle, possessions, attitude (Quote from someone) all belong to characterization?so please tell me the definition of characterization, and In some literatures, what's the purpose of characterization? To affect characters' personalities OR to get to the theme, surround the theme? Thank you for replying me!