That question is philosophical rather than scientific. You could find a lot of discussion of the matter if you visited philosophical sites like for example:

http://plato.stanford.edu/entries/life-meaning/

http://plato.stanford.edu/entries/reasoning-moral/

and other topics at http://plato.stanford.edu/

You have a choice of two things:

You could accept the word of some religious or political leader who tells you that he has the answer and says that you should go out and do things for him, like killing or destroying things, or you could work out for yourself what you value in life and what you should do about it.

I leave it to you to decide which you feel is better for you. Everyone must work out his own way, or else just take things as they come. Taking things as they come is the easiest way, but if you want to know where you are there is a lot of work for you to do. It does not help to be impatient. If it were easy, people would not have struggled to find the answers for thousands of years.

Some people say: "Then it is impossible. I will not live while struggling all the time. Why not die? That is much easier!" Yes, but as a famous American pointed out: "It is longer." While the challenge lasts you might as well show yourself, and show anyone who matters to you,  show them what you are worth, and do something better with your life than just making a mess of it. 

If you look around you and look back in history, you will see that some things are bad now, but many things are better than they ever have been. They are better because on average in every generation some people did more good with their lives than bad. I think it is worth trying to be be such a person.