This is the most basic of the crochet pattern stitches.
1. Make a chain of required length.
2. Insert hook through ridge in back of second chain stitch from hook.
3. Place the yarn over your hook; catch the yarn and draw it through your chain stitch. This puts 2 loops on your hook.
4. Place yarn over hook again and draw it through both loops on hook, completing one single crochet. To work single crochets across the length of chain, insert hook into the next chain stitch and repeat the single crochet steps above.
To continue rows of the single chain pattern:
5. Work a turning stitch by chaining 1, then raising yarn to the correct height to begin next row. Turn work around in order to work in the opposite direction.
6. Insert hook in first stitch of previous row and repeat the single crochet steps above. Do this in each stitch across previous row to complete another row. For subsequent rows, chain 1 and turn (step 5) and repeat step 6.
How to work single crochet - "sc"
Ch desired length.
Step 1 - Insert hook in 2nd ch from hook, y o as before. Draw yarn through the chain - 2 loops on hook - , y o, draw through both loops; one single crochet made. Work one single crochet in each remaining chain.
Step 2 - Ch 1, turn, work 1 sc in each st of previous row, inserting hook under both strands of st unless otherwise specified.
Repeat step 2 for desired number of rows.
Fasten off by breaking yarn a few inches from last st and drawing end through last loop.
Source: Crochet Primer, Bernhard Ulmann Volume 64