Not just Muslims, but every single human being has to answer the most fundamental question at some point in his or her lifetime:
"Why was I created? Why am I here? What am I doing in this world? Why did God create me?"
These questions are questions which each and everyone of us reflects on at some point during their life. We have some answers, which are given generally but usually these answers don't satisfy us - seeming somewhat simplistic. So, we still wonder: "Why me? Why here?". I know all of you (Muslims), are saying, "To worship Allah, khallas (finish). What more is there to say? Why do we need to have a big long talk on why we were created when we all know it is to worship Allah?!"
But wait. If this is presented to a non-Muslim, the next logical question would be, "Why does Allah want us to worship Him?" Then your stuck, which can only mean that in our own minds it is not really clear. Why did Allah create us to worship Him?