Okay. Where you are, unfortunately, Ash Die back disease has been discovered only last year, in June, 2014. If you want to make a bonsai out of your ash sapling, it is at great risk of suffering this disease - because its an outdoor tree, even as a bonsai it will need to be outdoors for most of the year, only being brought in if the weather is exceptionally cold and the plant is in danger of freezing solid. Which means it has no protection from Ash Dieback - for this reason, you might want to consider whether to proceed with your attempt at bonsai with this particular subject.
Otherwise, bear in mind that because Ash has quite large, compound leaves, its not the easiest of subjects to bonsai, and it can't be a small bonsai tree. The link below might be of some help, though I suspect they want you to subscribe to get information, but its probably best to buy yourself a Primer which contains instructions at a basic level, showing the equipment you'll need, etc.
Amazon appears to have a selection of books available on this subject, one of which, Bonsai for Beginners, does seem to advise on equipment and techniques. Bonsai from Native Trees and Shrubs, by Werner Busch also seems to include growing your own from saplings.