My crochet is rusty so if I'm wrong, I trust someone will point it out.
As this is around a slipper opening and probably is meant to reduce the number of stitches, you're working a decreased number of stitches.
Single crochet in 4 stitches, skip the next stitch and sc in the next 4 stitches, repeat around. In other words, work 4 stitches, leave one unworked, work the next 4 stitches, leave one unworked and so on. The skipped stitch will leave an eyelet and you'll have 1 less stitch for every 4 in the previous row. HTH
I should never overestimate my basic arithmetic skills.