To demonstrate, we will be working an example in single crochet.
Begin with your foundation chain as usual.
In the second chain from the hook, work 3 single crochet. Why three? The first single crochet will count as the last single crochet along the bottom of the chain (this will make more sense after you've worked the unused loops). The second single crochet fills in the gap between the top and bottom and serves to "fling" the stitches around the edge of the chain so that the work will stay flat. Sometimes this stitch is omitted when a cup shape is intentionally desired (for taller stitches, such as double crochet, more stitches may be required to fill this gap and keep the work flat). The third single crochet counts as the first single crochet along the top of the chain.
Next, single crochet as usual in each chain across to the last chain.
Work 3 single crochet in the last chain. Why three? For the same reason as above: the first single is the last single crochet on top, the second single crochet fills in the gap between the top and bottom, and the third single crochet is the first single crochet along the bottom edge.
Now you can rotate your work so that the bottom is now on top. The unused loops are the loops running along what is now the top of the work.
Then simply work one single crochet in each remaining unused loop across.
And that's all there is to working in the unused loops. Now that you know how easy this technique is, we hope you'll practice it with your very own pair of crocheted socks. Nothing is more cozy than a pair of handmade socks.