Crocheting question...

I have taught myself to crochet...which is fine, as long as you don't have any questions that aren't covered in the book... I have completed two of the 20 octagons I'm supposed to make for this afghan (let's not even talk about the squares). I like the colors and I'm having a reasonably good time. I've gotten so that I can follow the pattern and that's nice, but the central cluster is hard. Here's my question: Sometimes, I'm supposed to insert the hook into a space, instead of a stitch. My understanding is that the stitch is the 'V' part, the back of which is just a single piece of yarn. So, what's the space? Anybody?

Crap, I've just looked online to find that I've been picking up too much stitch. I have been picking up the entire V, instead of just one half...well, my octagons look like they're supposed to so...

The central clusters are really the problem. That link is a hexagon but my octagon is the same idea. The thing is, though, that for this hexagon, the person has started with a 6ch, which makes sense. Mine starts with a 5-stitch chain and is supposed to be an octagon. So, I'm having to make clusters in stitches, which is straightforward, but also 'spaces,' which confuses me...