If you look in the newbies for the fishless cycling thread it will explein everything you need to know about getting your tank ready for fish, good luck.
guppys can only put into a tank that has been cycled for a while and should be 1 of the last fish to add to you tank b/c of them being to sensitive, they can only be added to a new tank when youve used mature filter media to set it up with and then it should be after about 5 days before you do ideally.
if you havent used mature media then you need to add a couple of hardy fish into it when its cycled to mature it on for a while longer.