Knitting through the back loops? my so-called scarf

I am trying to start “My So-Called Scarf,” and I’ve realized that I have no idea how to knit through the back loops at all. What does that mean?

I am also confused by the pattern in general - it says to s1, k1, psso but before dropping the slipped stitch off the left needle, knit into the back of it. If I knit into the back of the stitch before I slip it, isn’t that just a knit stitch? I figured this might be confused because I knit Continental, but if I change “left” to “right” needle, then these instructions have me knitting with the left needle - is that right?

I figure I am missing something obvious, but any assistance would be much appreciated. TIA!

Normally you knit by putting your needle into the front loop of the stitch. When you knit into the back loop, you slip your needle in from right to left into the back part of the stitch.

sl, k, psso is a decrease. You slip one stitch from left to right needle, knit one stitch, then pick up the slipped stitch with the point of your left needle, bring it over the stitch you just knit and pass it off the tip of the right needle.