Whip and tongue grafting = joining a scion onto a rootstock with a particular shape of cut called a whip and tongue.
This method is a bit more fiddly than saddle grafting, but produces a more stable graft with better contact between the cambium layers and so it is more likely to produce a successful graft.
Whip and tongue grafting (YouTube, 3:33)
Have a go at whip and tongue grafting, being extremely careful not to cut yourself. You can learn the technique using any two twigs that are about the same thickness until you feel confident enough to have a go on a real rootstock and scion.
Search YouTube for ‘whip and tongue grafting’ to see some videos of practiced professionals carrying out this technique.