buttonhole on a baby bib

[STHLMgreen]

I am making a simple baby bib.

The pattern is located here: http://knitlist.com/2003/babybib.htm

I am confused by the buttonhole part (especially the bold):

Buttonhole row: Knit two stitches, yarn over, knit two together, knit one
Knit until 3 ridges show after buttonhole (5 rows)
Repeat buttonhole row
Knit until 3 ridges show after buttonhole (5 rows)
Repeat buttonhole row
Knit until 3 ridges show after buttonhole (5 rows)
Bind off remaining stitches

I can yarn over and knit two together (thanks to the helpful videos!) but don't understand. I could try and follow buttonhole instructions on another site but I want to lern to follow patterns.

Could anyone help with this?