All students should be aware of the need for referencing in its most academic sense -- the listing of sources which they cite in their work. (For a different type of referencing, used in applying for a job, see personal reference.)
Some teachers place enormous stress, time and attention on the subject of referencing, and so should you. It is one of the fundamental disciplines of worthwhile academic study. All academic work should be able to show that it is based on reasonable deduction from legitimate data. One of the practices it should encourage is that of careful attention to detail.
For scientists, the data is often from observation or from experiment. For other subjects, the data may well be from books and written sources. For worthwhile academic study, you should tell your reader where you got your data. This is partly a question of your professional training in the skills of judgement. Judgement is one of the skills that a University - and any worthwhile school - seeks to develop in all its learners.
There are many fussy details involved: for a start, every University department has its own rules, and for many departments these are unique. But they can all be viewed as boiled down to four Principles of Referencing, and the system your Department uses will fall into one the more important families of systems of academic referencing.
Other teachers will list a different number of 'principles of referencing', and define them in different ways. Read them: the different views and emphases will help you to learn better what you need to do.