How to do it
Ch 4, YO, insert hook in 4th ch from hook, YO, pull up a loop, YO pull through 1 loop on hook (ch made), (YO, pull through 2 loops) twice (first FDC made), *YO, insert hook into the ch made at the base of the stitch, YO, pull up a loop, YO pull through 1 loop on hook (ch made), (YO, pull through 2 loops) twice (second FDC made). Repeat from * until you have the desired number of stitches.
Visual Steps
Ch 4
Yarn over
Insert hook in fourth ch from hook
Yarn over
Pull up a loop
Yarn over
Pull though one loop on hook (ch made)
Yarn over
Pull through two loops
Yarn over
Pull through two loops (first FDC made)
Yarn over
Insert hook in the ch made at the base of the stitch
Yarn over
Pull up a loop
Yarn over
Pull through one loop (ch made)
Yarn over
Pull through two loops
Yarn over
Pull through 2 loops (2nd FDC made). Repeat from step 12