Ribbing is a stretchy fabric created by alternating knit and purl stitches across a row.
It is stretchy and does not curl, and is useful for cuffs and necklines.
When making ribbing you can use any repeated combination of knit and purl stitches, such as: (K2, p2), (k2, p1), (k3, p5), etc.
“Work (or continue) in ribbing” = “Knit all the knit stitches and purl all the purl stitches for as long as you want to maintain the pattern.”
For 1x1 Rib:
CO an even number of sts.
Row 1: (K1, p1) to end.
For 2x2 Rib:
CO a multiple of 4 sts.
Row 1: (K2, p2) to end.