Instructions on a pattern

Hi everyone,

I am trying to this scarf
but I am wondering what this means : Sl 3 sts tog purlwise WYIB
Any help would be greatly appreciated. Maria

You slip the needle into three stitches from right to left like you were going to purl except your yarn is in back like you were knitting. Don’t knit them though, just slip them from the left needle to the right needle.