K4 – knit 4 stitches
YF --move the yarn to the front of your work, as if you were going to purl (but don’t purl)
Slip 1 – slip one stitch from the left needle to the right needle, without knitting it
YB – move the yarn back to the back of your work
K5 – knit 5 stitches
…and so on. Does that make more sense?