Just as each of us has our own unique hairstyle or style of dressing, so does our writing.  Unlike hair and clothing, however, writing style has only two main categories: formal and informal.

Formal writing is very precise and the language, or wording in formal writing, is carefully chosen.  Also, no personal references (I, me, we, etc.) are used.  Informal writing is more relaxed and has a conversational tone to it.  It is more lively and personal and uses personal references.

The style you chose to use when writing an essay will depend on your audience and purpose.  For most school essays the appropriate style is formal.