when you slip a stitch, you have the choice to keep your working yarn behind your needles of in front of them.
If you keep it behind, then there is not a strand visible from that side (but from the other) and the other way around.
So, if that is the right side of your pattern that has that instruction, then the pattern wants you to lift a stitch upward, but not to run a strand across.
Are you an English knitter or Continental?
Whichever: just do not bring the yarn forward (as you would for a purl stitch) but keep it where you have it for the knit stitches.