I think the main point of life is to work hard, have a few laughs and at the end of the day be able to say "I enjoyed my life".
Oh yes and helping others and the world around you is an important factor in that too, I mean sure you could work hard transforming your backyard into 19th century Europe, have a few laughs pretending to be Napoleon and at the end of the day say "Being Napoleon was cool" but would it have improved the world or made others happy?
Well, without my ambition I'd honestly have no reason to live, but not many people are ambitious so I wouldn't call that for everyone. Although at times I can't help thinking that some people would be better off dead, as they have done nothing with their lives. Yeah, my ambition is the only reason I carry of living, and once I've reached my goals then who knows, I might just keel over.
Biologically speaking life is it's own purpose, and your only job on this planet is to stay alive and have children, so that your lineage will continue after you're gone.
Personally, I don't even think the biological purpose fully applies. While humans are still bound to many primal instincts (more than most of us think), we're often able to take a step back from them. An example here might be people who make the conscious choice not to have children, or who choose to adopt rather than create their own offspring.
So while technically our purpose is no different from that of any other organism, on a more personal, philosophical level I prefer to think that life doesn't have any point, goal, or reason. Sure, you can strive to be happy or to make others happy in a million different ways, and those are certainly Good Things, but there's nothing saying that that's what you're supposed to do. I think that life itself has no meaning, because that leaves you free to find your own meaning. If you find meaning in helping others, that's great. But if you find meaning in earning as much money as you can, that's just as good (in this context, at least). If you don't find any greater meaning at all and are content in just living your day-to-day life, again, that's just as good an answer as anyone else's. The point isn't to find the 'right' way to live, but simply to live your way.