Change pattern to circular?

Can someone explain to me how to change a pattern that is for flat knitting into circular?

This is the pattern I want to use (I want to make a shopping bag), but I have no idea how to switch to circs.

Cast on an odd number of stitches.
Rows 1 and 3: Purl.
Row 2: K1, *yo, k2tog, repeat from * to end of row.
Row 4: *Ssk, yo, repeat from * to last stitch, k1.

Repeat Rows 1 - 4.

This is probably extremely easy and I will be embarrassed when you all tell me how it works, lol. Thanks!

Rows 2 and 4 will stay the same.

Rows 1 and 3 will be knit instead of purl.