To decrease, you crochet more than one stitch together. The one I use the most is crocheting 2 single crochet stitches together.
1. Insert hook into next stitch and draw up a loop:
2. Insert hook into next stitch and draw up a loop:
3. Yarn over and draw the yarn through all 3 loops on the hook:
This is what it looks like after completing 3 more sc2tog:
Begin with row of 6 chains, insert hook into second ch from hook:
Yarn over and pull through both loops on hook for a single crochet stitch(sc):
Insert hook into the next chain, yarn over, pull through both loops on hook 4 more times and you have a row of 5 single crochet stitches: