2.  Depending on what kind of paper you are writing determines which format you use. Your professor or teacher will also direct which format they want to see.  MLA : Modern Language Association (of America).  format used for essays that are focused one literary criticism and/or analysis.  APA : American Psychological Association  scholarly, scientific journal articles are written in this format  Works often are meant for publication

3. Academic Disciplines geared toward MLA*:  English  Mass Communication * Academic Disciplines geared toward APA*:  Criminal Justice  Education  Engineering  Psychology  Most all Sciences

4.  No each style has a handbook to use as reference.  You will focus on page formats, citing works, in text citations and general formats.  MLA Handbook for Writers of Research Papers. 6th ed.  Publication Manual of the American Psychological Association 5th ed.  Both can be found online or at a library