What Ingrid said, YF is between knit sts, YRN is from a knit to a purl, YON is from a purl to a knit. But they’re all YOs. There’s also a glossary on the site - www.bernat.com/glossary
So does this mean I am executing them differently? For example, I would bring the yarn over the needle from the back to the front on one and then from the front to the back on the other?
YEs, it describes what you do with the yarn based on the stitch you just did and which st you need to do next. It can be very confusing if you’re not used to it. It’s common in british patterns and older US ones.
Here is a really good article explaining the whole issue of the different designations. LINK The part that starts something like, “So, um, what is this yfwd thing?”, will be of interest.