That's a good video, but I'd warn against many of the other youtube featherstick videos. More than one shows feathers with no curl to them at all!
1.)Kneel on the ground
2.) If you've batoned wood in half to get to the dry stuff, you'll already have a flat surface with a 45 degree bevel. If not, carve the wood until you have this surface to work on.
3.) Hold the top of the stick in your non dominant hand, with the other end of the stick on the ground.
4.)Hold your knife in a "hammer" grip. As you start to carve the feathers, there should be more pressure applied keeping the blade close to the stick than pressure pushing the knife down, if that makes sense.
5.)Try and maintain the same angle all the way down, so the blade doesn't bite too deep. This will allow you to create long curly feathers.
6.) Tilting the tip of the blade up or down with each feather will allow you to use a slight slicing motion with each cut, this also creates numerous curls that spiral off to one side.
7.) I keep my arm straight when feathering, pushing down with the shoulder and upper body. I feel this gives the best control.
8.) Once you have completed a feather, twist the knife blade so that the feather is pushed up almost 90 degrees to the stick, this means you'll be less inclined to cut off your other feathers each time you carve a new one!
9.) I use the tip of my blade to carve tiny feathers which will light from a firesteel, igniting the larger feathers. Aim for 3 to 4 curls per feather.
Hope this is clear and helps!