To make a yarn over (abbreviated yo) when it goes between 2 knit stitches (which you’d encounter in a pattern as k1, yo, k1), follow these steps:
Knit the first stitch.
Bring the yarn forward between the needles into purl position.
Knit the next stitch on the needle.
When you knit the next stitch, the yarn automatically crosses the RH needle, forming a yarn over (see the figure below).