Here's how it works:
Direct from MSN 
"when it comes to almost the end of winter
which is almost the start of summer
a designated day would be chosen
on that day, at 2am in the morning you move the clock one hour
ahead, i.e 3am
you lose on hour
when autumn starts in march the next year
you choose a designated day again, and move back the clock at
2am
so u gain back one hour
in summer till spring, ie. nov till march
we have long days, sun sets at say 8, 9?
in winter we have short days
sun sets at say 4,5"
This is based on Australia but the concept is there 
