i don't understand slipped stitches.

[christy_cooper]

"slwyif: bring yarn to front, slip 1 st purlwise"

This brings the yarn in front of the slipped stitch; it's a decorative treatment. Sometimes it's used for a "wrap and turn" type of short-row (this is how you wrap a knit stitch at the end of a row).

[stripey_cat]

You get a horizontal bar across the front of the slipped stitch.  This can make really cool woven-looking patterns in your cloth.  In this pattern, I think it makes that edging that looks like textured braid.

[RomBookLover]

It's decorative and keeps the edge from rolling.