When I first started doing YOs it was hard for me too. Finally I gave up trying to follow instructions and just looked at the yarn, and made it go over the needle once and be at the front for a purl or at the back for a knit. Once you can get it to work and do it a few times, it should be fairly easy to repeat and soon you'll not have to think about it. I could sit here and look at how I do it but I don't know if even then I could tell you how. Maybe I don't even do it right, but the end result looks and works right.
I should never overestimate my basic arithmetic skills.