Citing the sources of information you used is not really hard; it just takes a bit of time. There are many different citation styles, but most students need to learn to follow the conventions of only MLA or APA. Style guides are about more than just citing sources of information or ideas. Guides can help you improve the style of your writing and avoid bias, for example.
Any citation you provide should enable your reader to find that source. Make sure your citation gives the reader the information he or she needs to find the source you used.
MLA Handbook, 9th edition by 
MLA Style Manual and Guide to Scholarly Publishing (3rd Ed.) by MLA style is used mostly by students of the humanities, particularly English, comparative literature, and the performing arts. MLA puts out two publications, each of which cover more or less the same material, but with slightly different emphases. The MLA Style Manual is geared more towards graduate students and faculty. The MLA Handbook, more well known, is usually the choice for undergraduates.
Most of the major style guides can be found at Pace University's Campus Libraries. Information you need to locate the books (call numbers and locations) can be found here. Ask at the circulation or reference desk if you're having trouble finding a book.
