Start in the place your puppy has had an accident. Make sure you clean the accident up properly with neutraliser and put a puppy pad down in this area. As puppies always wee where they can smell where they last went, using a small amount of a used training pad will encourage your puppy to wee on the new pad and therefore where you want them to go. To do this cut a small piece of the old pad out and place it underneath the new clean pad.
Once your puppy knows to wee on the training pad (and only on the pad) you can gradually move the pad closer to the door until you can eventually put it outside. Only move it by a few inches at a time. Your puppy is now (barring the odd accident) toilet trained.
If you want them to wee in a specific area of your garden you can use the used training pad and move this to where you want the dog to wee. If your puppy asks to go out for a wee, take it outside and stand with it where you want it to wee until it learns this is the right place. This may take a bit of time and accidents will happen.