You put your right foot on the right pedal and your left foot on the slave? When you push down the beater will hit the drum head....doubles will allow you to do this with both feet? I dunno mate, what on earth do you want to know that you can't find out by searching through one of the 16,567,980,923 existing double pedal threads here on DW?
If you have something specific, by all means ask.....if not, go play the damn things man. It ain't rocket science, you put your feet on them and play. Adjust the set up to suit your own comfort........just like you would on a single pedal....only now you have to do it twice.