A reference providing information about where a particular quotation, text, etc., is to be found; a bibliographical reference. [Oxford English Dictionary]
In general, citations help readers to locate your sources of information, as well as avoid plagiarism.
Understanding and avoiding plagiarism
You need to understand why and how to use citations to help you avoid plagiarism! The Online Tutorial on Academic Integrity has been developed to raise students’ awareness of academic integrity and the University’s expectations for honest academic behaviour. Use this interactive tutorial to understand the importance and mechanics of avoiding plagiarism through proper citing.
The Library offers several reference management tools: EndNote, Mendeley, and Zotero (which are freeware). Understand the features of these tools from this page and choose a proper tool to organize your citations and references. Refer to this EndNote FAQ if you encounter any problems with EndNote.
Which citation style shall I use?
The citation style you use depends on your discipline. If you're not sure, check with your professor. Citation styles commonly used by various disciplines are listed below:
IEEE Style is a numbered style with two components: in-text citations (placed in the text), and a reference list (at the end of the text). The citations in the reference list are numbered and appear in the same order that they appear in the text.
Two parts of a citation:
1. In-text citation
Each number is enclosed in square brackets, e.g. 
Once a source has been cited, the same number is used in all subsequent references.
The given name of the author or editor is abbreviated to the initial regardless of the presentation of the author's name in the source document, followed by the last name.
The title of the book or journal is in italics.
The title of an article (or chapter, conference paper, patent, etc.) is in quotation marks.
“IEEE publications must list names of all authors, up to six names. If there are more than six names listed, use et al. after the first author. For non-IEEE publications, et al. may be used if names are not provided.”
J. S. Scott, Civil Engineering. London, England: Longman, 1969.
Two authors or more
J. G. Teng and J. M. Rotter, Buckling of Thin Metal Shells. London, England: Spon, 2004, pp. 55-70.
C. H. Chen, Ed., Image Processing for Remote Sensing. Boca Raton, FL, USA: CRC, 2008.
Two editors or more:
T. W. Hertel, S. K. Rose and R. S. J. Tol, Eds.,Economic Analysis of Land Use in Global Climate Change Policy. New York, USA: Routledge, 2009, pp. 32-33.
Chapter in a book, one editor:
W. F. Caspary, Concepts of Network and Deformation Analysis, J. M. Rüeger, Ed. Sydney, Australia: School Surveying, Univ. New South Wales, 1987.
T. A. Davis, User Guide (Version 4.0), 2002. [Online]. Available: http://www.cise.ufl.edu/research/sparse/umfpack
R. J. Hijmans and J. van Etten, “Raster: Geographic analysis and modeling with raster data,” R Package Version 2.0-12, Jan. 12, 2012. [Online]. Available: http://CRAN.R-project.org/package=raster
S. Yhann and J. J. Simpson, "Application of neural networks to AVHRR cloud segmentation", IEEE Trans. on Geo-science and Remote Sensing, vol. 33, no. 3, pp. 590-604, 1995.
G. X. Liu, X. J. Luo, Q. Chen, D. F. Huang, and X. L. Ding, “Detect-ing land subsidence in Shanghai by PS-networking SAR interferometry,” Sensors, vol. 8, no. 8, pp. 4725–4741, Aug. 2008.
Published Conference Proceedings
N. E. Huang, Z. Shen, S. R. Long, M. L. Wu, H. H. Shih, Q. Zheng, N. C. Yen, C. C. Tung, and H. H. Liu, “The empirical mode decompo-sition and Hilbert spectrum for nonlinear and nonstationary time series analysis,” Proc. R. Soc. Lond. A, Math. Phys. Sci., vol. 454, pp. 903–995, 1998.
IEEE Criteria for Class IE Electric Systems, IEEE Standard 308, 1969.
Letter Symbols for Quantities, ANSI Standard Y10.5-1968.
Citation link on databases
Many databases provide quick link to citation style, you can simply "copy" the citation from your search result list and "paste" to your document. The following are a few examples of copying APA citation (6th edition) from online sources: