I'm currently working on a lovely pink tunic sweater for my daughter and the pattern said to do a provisional cast on, which I had heard of but had never done before. Thanks to the wonderful world of YouTube I found this very helpful tutorial and I thought others may be helped by this as well.
The provisional cast on method is helpful when you want to have live stitches left at the bottom of your work so you can add some kind of edging later. You cast on the needles with some scrap yarn and knit your work onto that. Then when you're ready to have those stitches available to work on you simply remove the scrap yarn and you have your live stitches, rather than having to pick up stitches later. You'll need your knitting needles, some scrap yarn and a crochet hook to do this method of casting on.