When one user begins to communicate with another user about some subject, they start to form their understanding and cognition towards this affair. Whether the cognition is right will influence people who are involved in it. After that, in order to get insighted into this phenomenon, some reasons would be given and some theroies would come out.
From my perspevtive, social media are the medias where social network exists. In one network, people form an idea towards one person or thing, and change their idead through their interaction. Take Weibo for example, firstly, people make friends, express their ideas through writing some articles or sending a few photoes with some comments. When others see these articles and get the core information and transfer the word information to their personal thoughts towards ont thing. After that, these comments then can be further broadcast and spreaded. Information exchange is the fundational function of social media.