A bibliography is a list of citations to books, articles, and documents. There are several reasons for citing sources:
- to respect the intellectual property and the laws on copyright;
- to give the reader the possibility of finding the original text;
- to provide support or evidence for what the author says

There are lots of different methods of writing bibliographies. Some suggestions:

How to cite a text (in italian)
Tutorial (in italian)
Reference management softwares