There is a huge difference in watching a lot of videos, and doing. It's not just the theoretical knowledge that's necessary, it's training your hands and co ordination for the task. That you can only get through physical practice. Sewing machines are their own beast, and whether you're sewing fabric or leather, there can be a pretty steep learning curve there as well; the difference with with fabric is you can always pick apart a bad seam and re-do it, with leather, you get one shot.
My suggestion is pick the simpler of the two, then make it. Then make it again. Then make it again. Then make it again. By the 15th one or so, you may have something that comes remotely close to the one in the picture.
That's my two cents
Tinkerton