I think it is difficult to know what you want to do with your life. I feel it is a process -- you start doing something (anything) and you learn and discover a purpose and direction along the way.

When I was at my university, I took a test that measured my interest in different careers. Based on my answers to the questions, it ranked professions that I would most likely enjoy to least likely. I found it helpful because it listed several professions I hadn't thought about and the one I was pursuing was actually in the middle of the list. After seeing the results and thinking about it for weeks, I decided to drop my current major and pursue a different degree that fit professions closer to the top of the list. I got that degree and glad I changed. It hasn't been a perfect career and I am always thinking about other related jobs and careers that I could get into in the future. I feel like it gave me a good start.

There may be similar interest tests online.