Question about 'time dilation'?

This says that the closer you go to the speed of light, the more time slows down for you compared to others. So you'd go 99.9% the speed of light and you'd get to a star pretty "quick' but when you return to earth they'll have aged more than you, at least form what I've heard. That makes sense to me BUT if we actually had a 'spaceship' that could go at 99.9% that speed of light, I'm pretty sure that the HUMANS that planned the trip would be monitoring the ships progress. Yes, monitoring the ship. When they look at the ship they would see that it takes a hell of alot longer than they expected it too, when in reality its already been there and back? The people who planned the trip would be watching it for 4 years(let's just say that it was 4 light years away) and watching it return for 4 years, where in this whole thing do the people who are monitering the ship get older? This whole 'time dilation' theory makes no sense.