I was worried there when someone said that my description of leg yield had the driving leg mixed up. Even if I had never read a website instruction, my instinct would be to have the inside (driving) leg at the girth and the outside at a supporting position (passive) behind the girth to guard the hindquarter from slipping out.
In reality , driving legs (the one that creates the imputus) are almost always at the girth . That's where there is a bundle of nerves (can't remember the name) that makes it a very sensitive area and automatically will cause the horse to want to move, have imputus.
The leg yield is MORE FORWARD than sideways. you might even think of it as 2/3 forward, 1/3 sideways. Don't think sooo much of sideways.
However, the aid for sideways is applied rythmically, with each step and then you STOP applying that leg and think Forward! Or rather you support the horse with forward , such as kind of holding the outside rein .
As for your confusion of inside and outside. The inside is always on the inside of the very small arc you create with your bend. So, you are mvig your horse to the left but since you have bent him a teeny tiney amount to the right, your RIGHT side is the inside. And don't be fooled by focussing on the rail for inside/outside. You'll get used to it.
When you try LY with your horse, try for just one step over, one forwrad, and one over, then drop the contact (and I mean to on the buckle loose) reach forwared and pat that good horse. He did what you asked. Remember that you are learning/teaching. Doing one or two steps correctly is what you are after for the time being. You need to give a big release and praise for your horse to know he did it!
I do one or two steps of LY on the trail all the time and them a big "good boy!' Horses need that release to know they did the right thing.
As far as canter goes, I learned the way others have described as a beginner method. I still use that, and actually, I am still a beginner in that respect. One thing I read and have found to be true in actual practise, is that if your horse swings his hindquarters inward as many are want to do due to natural crookedness, canter on for a bit and instead of trying to push his hindquarter back to the rail, thing of shifting his shoulder over to that they track in front of the hind legs, where they should.,
Also, if you guys are learning canter depart, than reward your horse after just that: CANTER DEPART. At least at first.
After a bit, then you canter on and work on the quality of the canter.