So what does it mean to crochet in the bump or ridge? It's really quite simple. Once you have your foundation chain, you'll insert your hook into a chain stitch and crochet a single crochet, double crochet or whatever stitch you are working with. And this makes a neat loopy sort of edge at the bottom of your piece. Ever notice that when you finish a piece though, the top doesn't have that edge? That's because you didn't crochet in the bump, so the top and bottom edge of your work don't match. Which isn't necessarily a problem if you're going to add on an edging anyway, but when you crochet in the bump, you turn that starting chain over and there's a little bump or ridge on the back of each chain. Insert your hook into that bump and crochet your stitch. You'll see the difference at the bottom of your work immediately, as it looks more like a V. When you complete your piece, the top will match your bottom. I've found this useful for simple pieces like scarves when I'm not adding on an edging or broader. I've added a video from YouTube to demonstrate this and I hope your find it helpful!