Generally, a reference list contains only those sources you actually referred to within the body of your assignment. So, for each resource on your list, there will be some citation/reference in your assignment. Your marker will check these off as he/she reads through your work
A bibliography, sometimes, is taken to be a list of all those sources you looked at for the assignment. This list, also attached to the back of your assignment, contains all those books, articles, website, and so on, you cite in your assignment but also those ones you consulted but didn't actually cite/reference within your assignment.
Your lecturer will indicate whether they wish to have a reference list and a bibliography attached to the back of your assignment. However, in the main, most subjects require only a reference list. If you are unsure, check with your lecturer.