Okay, major pet peeve time:
SO MANY learn-to-knit resources, be they videos or books, explain yarn overs in a way that is confusing and leads people to think that the stitch after the yarn over is actually part of the yarn over. Usually it's something like "bring the yarn to the front of the needle, knit the next stitch." Which, if you're knitting English style, will cause you to sort of half-accidentally make a yarn over followed by a knit stitch.
This is annoying for several reasons:
1. That is a "yo, k1" NOT a "yo", and therefore will totally throw off your stitch count.
2. It really only works if you knit English style
3. You don't HAVE to follow a yo with a knit stitch. It could be followed with a purl, or a decrease, or... anything, really.
I guess the people teaching think this method is easier to demonstrate/explain than just... wrapping the yarn over the needle. But I get sooo many emails from frustrated new-ish knitters (or new to yarn overs, anyway) wondering why they aren't getting the right number of stitches and it is almost always because whoever or whatever taught them to yarn over, taught them using this flawed method and they are actually doing a "yo, k1" whenever the pattern says to do a "yo." Back when I worked in an LYS, we had a lot of customers with the same issue. It's a downright epidemic of misinformation! So, I figured a video tute was long overdue.
(BTW, if my tone sounds exasperated, it's not because of you, dear knitter, but because of all the instructional resources that should really know better. Don't set beginning knitters up for unnecessary frustration! Geez!)