The field of communications has to do with TV, radio, print media, the Internet and other ways that people share information with each other.
The word communicate should be a big clue to what communications is all about. Communications involves all the ways people get information and entertainment to each other. A communications major in college might major in journalism, broadcasting, or something else related to "getting the word out" (maybe even social media). Without communications — also known as media — we'd have no clue about the things going on in the world.