I've more commonly seen this as sl2, k1 , p2sso (slip the two stitches together as if to k1tog), but I guess there's a reason they want you to do them one at a time. It's not hard, but the p2sso can be a little tricky if your stitches are on the tight side.
There's a video here
that shows the SKP decrease, which is similar. The only difference is that in the video, she's only slipping (and passing over) one
stitch, where you'll be slipping (and passing over) two