Understanding psso in pattern

Hi, I’m hoping someone can please help me with a technique I haven’t tried before.

Cast on 60 sts
Row 1 knit
Row 2 knit
Row 3 k2, (yo, sl 1, k2, psso) 19 times, k1
Row 4 purl
Row 5 k1, (sl 1, k2, psso, yo) 19 times, k2.
Row 6 purl

Repeat from * to * five times in total.

So my question is…is passing a slipped stitch over supposed to decrease my stitches?

Yes the psso is a decrease but you are also doing an increase with the yarn over so your stitch count remains the same

This video shows how it to do it.
How to: Sl1. K2tog. Psso.