I’m using US terms.

what you can do with it:

Puff stitches are one sided — they do NOT look the same on the back!  Therefore, keep this for projects where only one side is seen.

how to do it:

If you want to do what I have done in the above picture, interspersing each puff stitch with a hdc, chain any odd number +2.  We will start in the third ch from the hook.  Yo, put hook through the third chain, pull a loop through.  You’ll have 3 loops on your hook total.  Yo, put hook through the same ch, pull another loop through.  Do this a third time.  You’ll have 7 loops on your hook total:

Yo and pull it through all 7 loops.  Ch 1 to close the puff:

You’ve made a puff stitch!  I’ve done this little swatch with a row of hdc in between the puff rows.