MLA style is a set of documentation guidelines used primarily for works about arts, languages and humanities. If you've used other styles (like APA), MLA style will probably seem much simpler and more intuitive.
Using MLA style property enhances your argument by properly citing and using source materials, or previously written works. Maybe even more importantly, proper usage of MLA style--particularly citations and works cited pages--will protect you from being accused of plagiarism--whether intentional or unintentional.
What is a citation?
A citation is a short description of a specific information source that is used to give credit to the original author(s) and also provide information to find the original source.
What is a works cited page?
A works cited page is an alphabetical listing of the sources used in a paper (listing only the works that you have actually cited).
What is a bibliography?
A bibliography is like a works cited page, except the bibliography lists ALL sources used to write a paper, not just the ones cited. Typical MLA styles does not call for a bibliography (just a works cited page), unless your teacher asks specifically for a bibliography.
Source: http://www.mla.org/style
Setting up your paper:
The first page:
Here's an example of the first page of an MLA-formatted paper. Note the double-spacing and name in the header.