INFJ stands for Introvertive, iNtuitive, Feeling, Judging
The Myers-Briggs is a personality survey, meant to give you and others a little bit of insight into what your personality is like and how you react to things.
The Introverts, compared to extroverts, generally "recharge" themselves by quiet activites. Do you generally like to stay home or hang out with a small group of close friends, or are you the type that goes to bars and clubs?
The Intuition type is balanced with the Sensing type. Intuitive types trust hunches and theories, while Sensing types like facts and data that can be backed up.
The F stands for Feeling, and it's opposite in this test is Thinking. Thinking types make decisions from standing back and using logic, while Feeling types use their emotions and empathy to chose a best course of action.
The last category is either Judging or Preceiving. The Judging-Perceiving relationship relates to the dominant side of the brain. Judging is generally associated with left brain dominance, and Perceiving is associated with right brain dominance.
You might find this page helpful in understanding your personality.
http://www.personalitypage.com/INFJ.html
Remember, it can sometimes change, and that's okay. As you mature throughout your life, your views may shift slightly and you might see the world and yourself in a different way.
I wouldn't look too hard for a quick answer to see if you're bipolar or not online. There is no site or counselor that can diagnose you in this manner. If you want more information on biopolar disorder though, try going to NAMI.org