How do they do it?

I`ve been following the progress of the Supergeese on Springwatch on the BBC television, and how amazing it always is to me that birds fly so far, and how do they know the way? Even, so the programme said, chicks that had hatched this year of some species of birds would be migrating many hundreds of miles on their own.

But, my question is, how do they know where to go, and when, and how?
Another of the wonders of nature isn`t it.