Darning in your edges is just another way to weave in the tail ends of your yarn when you're done with a project. I can't link to it here from work, but www.knitty.com
has a good article on it. Or check out Amy's video of a small project.
As for the crochet, I don't know if I could describe it here, but Googling crochet instructions will find you tons of sites.