Please, please let me in to the secret world of grafting!

I recently started to add some new trees to my small stock list and some are grafted (Paul's Scarlet Hawthorns, for instance) twice. The first graft is as it should be, at the base. But on some there is a second, new graft at the top on the main leader. The trees are 6 to 8 feet tall and the second graft is a couple of feet from the tip of the tallest part. What's it for?

My other question is how do I start some Paul's Scarlet off on my own rootstock? I've never grafted before, so read up a bit and all I know is to use some strong rootstock (in this case plain hawthorn?) and the Paul's Scarlet is coming from a large shrub at the back of my house that looks very healthy. Am I too late to cut from the PS now? I read that the two should be put together just before leaf break on the rootstock, but it didn't say what binding to use and I'm wondering what everyone else uses?

Advice, please, as it all seems very scientific to me!