MLA = Modern Language Association
This citation style is typically used in the humanities, but can be used in other subject areas.
The current edition is the 9th edition, so make sure you format your citations in the appropriate edition format that your instructor or professor requests.
MLA Handbook [9th edition] by 
MLA Handbook [8th edition] by 
Cite Right : A Quick Guide to Citation Styles - MLA, APA, Chicago, the Sciences, Professions, and More by 
Everything you need to know about MLA citations [electronic resource] by 