What does it mean when a knitting pattern says to WYF slip next 7 stitches?

You probably are doing knit stitches so the yarn is at the back of the project. Move the yarn to the front (as if you were starting to purl) and move the stitches from the left needle to the right needle (if you are left handed from right to left). Then continue your project accordingly.

WYF means "with yarn in front"