This is how I do the popcorn stitch.
It is worth noting that I use only 4 double crochet stitches to make my popcorn stitch,
when the usual is 5 double crochet's.
Step 1: in my project, I needed 1dc, 2dc, 1dc, popcorn stitch.
The arrow in the picture below shows where my popcorn stitch is going to go.
Step 2: make 4dc all in the next stitch, as shown below
Step 3: turn your project over to the wrong side (WS). You can see the WS view in the picture below. To complete my popcorn stitch, I sc in the top of the first stitch (from the WS)
sc in the top of the first dc as mentioned above.
Step 4: turn your project back around to the right side (RS). The photo below is how my popcorn stitch looks. The next stitch to dc into can be a little hidden, so I've put an arrow showing where my next dc will go.
Below is my finished round with 8 popcorn stitches.
(The one under the hook is a little hard to see on that angle)
It is also worth mentioning that a popcorn stitch is counted as one stitch.
When you are crocheting the next row, make your stitch in the sc at the top of the popcorn stitch.
Hope this has been helpful.