Citing your sources while writing your paper is standard practice in academic writing. The video Citation: a (very) brief introduction (1:54) explains why and how academics cite.
To make a correct entry in the bibliography at the end of your paper, you need to provide a lot of information about the source publication. For most journal articles this information is found on the first page of the article and for books on the front and back (verso) of the title page.
In the exercise Article reference you have to match the component parts of a reference in APA style (6th edition) to the information elements required for a correct entry in the reference list.