Moss stitch is similar to rib in the sense that you knit 1 & purl 1 however after the 1st row instead of knitting & purling where you did so before you do the opposite.
Cast on your stitches.
Knit 1, Purl 1 repeat across the row.
On the next row knit where you’ve purled & purl where you’ve knitted repeat this across all rows.
This creates a bobble affect called Moss Stitch.