As you'd be aware, when you cite a reference in a paper or thesis you need to follow protocols that are determined by particular formatting styles, e.g. APA1, Harvard, MLA and so on. These determine how you format the reference in the text and the format in the list of references at the end of the paper or thesis. In order to do that you need some way of keeping the data for each reference source you may wish to draw on in your writing.
You have a number of options here.
You could do it manually, i.e. keep a word processed list and then copy and paste from this list of formatted references2. This method can produce errors and you can't be guaranteed that all of the work that you cite has been referenced as is the case if you use bibliographic software.
You could use software to store this data. If you use software there are a number of options to choose from.