When you create something it is your own and yet it is shaped by the experiences of your past which usually include the creative work of others. Often structured learning experiences involve exposure to the creative output of others, when you read a book or listen to a lecture, for example. Today you are in fact bombarded with stimuli, and even in a fairly traditional classroom setting, many different modes of learning are going on. The result often is information overload. You need to sort out what it is you can say you know from what it is you are expected to learn.
When you get involved in a discussion or an experiment you automatically draw on past learning experiences to help you understand what is happening or being said and that requires you expose your mind to the history of ideas and to the ever expanding universe of human knowledge. In the process you will read the words written and absorb the images creatively produced by others. Therefore, in your own course of study you will need to refer to sources of information and grant appropriate acknowledgement. This is what is meant by academic integrity. You are honest about what you have consulted or cited in the course of your research. Shakespeare may not have invented the words, "To be or not to be?" and yet it is one of the most famous things he wrote. When you use it in reference to the line given to the character Hamlet you must give proper attribution. That includes the venue. Are you quoting a film version, a stage production or a paperback edition of the play? What act and scene is it from?
Many times you may still think of citations as having to do with only books. But that is just one context from which you may draw a quote or even just an idea. The World Wide Web is a virtual electronic network of "pages" that you can also learn from and therefore may also require attribution. Common knowledge is information that is freely available and was not produced as the intellectual property from the work of individuals. Just because something is on the Internet it should not automatically be considered "common knowledge." Common knowledge is a phase used to denote information that does not belong to any one individual and can be verified in many different places. There are legal and academic debates about our culture turning creative output into intellectual property, but the facts and opinions you obtain from others must be granted proper attribution. Unless these facts and opinions can truly be considered common knowledge, you are responsible for informing your reader where you acquired the information.