Haha, I've asked this question before :D Being alive , you have life in you, yet you're not even happy, you wake up, and just go about Truly living, is when you really have happiness, you are enjoying yourself, you have your own priorities, you've set goals, you know what to do with yourself...YOU'RE HAPPY! (My opinion )
Not much if anything. It is relative. If you're alive physically you are truly living. That is a materialistic term. People who are paraplegic or living in mud huts are "truly living" their lives.. I dislike that distinction as much as I dislike the term "get a life".
To be alive is going though the emotions of life. To truly be living life is to know what your destiny and purpose of life is and can only be found in a relationship with The Lord Jesus Christ our Lord and Savior.