This isn't so much a question, but looking at the other two questions that have been posted here from users who (like me) had a little bit of a tough time following this one - not because of any lack of information on Kent's part - it's not that at all, but simply because there was one button I personally didn't press - I just wanted to post my experience here just in case anyone else finds parenting the eyes to the bones correctly difficult like I did.
Essentially, when Kent explains to parent the eye objects to the armatures, whenever I tried to do this, I'd find that when I went back to the Modifier tab for the eyes, the armature modifier wouldn't appear, and the eyes wouldn't move correctly. This is essentially because I wasn't selecting the eyes themselves, before going into Pose Mode to parent the bones.
What I found worked was selecting the eyes in Object Mode, SHIFT selecting the eye bone armatures (still in O/M), and then go into Pose Mode (P/M) from there and parent the object up to the bones. I wasn't pressing Shift to select both.
When I did press shift to select the armature, as well as the eyes in O/M, it appeared to select the whole armature, which I thought was wrong - it doesn't, as soon as you go into P/M, it'll only be the bones that were selected before in P/M. You can use shift+click to remove selection from the head bone (if it's still selected from previous parenting) or add the other eye bone if only one is selected - and it doesn't matter which one is left active. From there, continue with the parenting.
I also thought it was wrong when it seemed that the eyes only moved along one axis (I also ran into the problem that for some reason my eyeball was parented to the mesh, but I think that was from where I got lost along the way and clicked the wrong place, easy enough to fix by just clearing the parenting of the eyeball and mesh in object mode), but after switching the pivot point to the median, and then pressing R TWICE to rotate freely, I realised I'd done things right and it was working, yay!
I've just undone it and redone it a couple of times to test it to make sure that's where I was going wrong, so I thought I'd post my results here just in case someone else has a similar problem. Sorry if it's in the wrong place, but as the Questions section is the first place I check if I'm stuck, I thought I'd post my own experience and solution to the problem here in case it's of any use to anyone else <3
