There are three ways to use refences in your text:
When you are using sources you have to do this accurately and in an above-board way.
When you use other people's work, you must state the exact source and author(s). Scientific advances are seldom achieved by one person alone. They are the result of work by many people, who deserve to be named when their contribution is used.
You use references so that others can see on what information you have based your work. They must be able to access the same information.
Quoting means repeating or copying out someone else’s words. You should quote when a formulation is so precise that it would lose its meaning or significance if worded differently.
When you quote someone else’s work, you must put the quoted text between quotation marks and provide a reference in the text and add the citation to your reference list.
Paraphrasing is rewording passages from other people’s publications in your own words. When paraphrasing you are not copying the text literally, but re-writing it. Paraphrasing is common practice in the scholarly texts. You introduce the concept that you found in the source and explain how you will use it in your essay.
When you paraphrase someone else’s work, you provide a reference in the text and add the citation to your reference list.
In the academic world there are strict rules for setting out source references. Each discipline has its own citation style. Also, references are set out differently depending on whether you use them in a bibliography, in the text itself, in a footnote or in an endnote. During your study you will learn which citation styles should be used for your discipline.
Some examples of citation styles, in this case for a journal article:
HAUCK, MARKUS. (November 01, 2009). Global warming and alternative causes of decline in arctic-alpine and boreal-montane lichens in North-Western Central Europe. Global Change Biology, 15, 11, 2653-2661.
HAUCK, MARKUS. 2009. "Global warming and alternative causes of decline in arctic-alpine and boreal-montane lichens in North-Western Central Europe". Global Change Biology. 15 (11): 2653-2661.
HAUCK, MARKUS. "Global Warming and Alternative Causes of Decline in Arctic-Alpine and Boreal-Montane Lichens in North-Western Central Europe." Global Change Biology. 15.11 (2009): 2653-2661. Print.