First, you must become a commissioned officer.  Look into ROTC (within your college) or Officer Training School after graduation.  If you have an Air Force or Navy ROTC unit at your school or if your school has a cross-town agreement you can join there.  ROTC would add some classes to your schedule and you would need to do some training in the summers.  If you want to be a pilot, you need a to get a pilot slot out of your class.  The best way to do this is be high up in your ROTC units order of merit.  It is based off of your GPA, Fitness tests, and commander's rating.

You could also apply to a Service Academy, but since you are in college already, beginning a four year school might be repetitive.

Pilot training is usually 1-1 1/2 years.  It can be a very stressful job in that you must be able to quickly diagnose and correct problems in mid-air.  The emergency procedures are extensive and must be memorized exactly.  You will also have to deal with potentially long briefings, de-briefings, and ground-based duties.  It is definitely NOT always "Top-Gun" hollywood glamor.