How Do I Add

A satin backing to a baby blanket I am making. I want to cover the WS with satin. How do I do that!?

block the blanket.

measure carefully

cut the satin, and sew!

(you might want to cut satin on bias, to give it more ease.)

you might also want to only line the center (if the blanket is knit with a garter stitch or sead stitch border, line up to border, and not the whole blanket.

if the blanket is all stocking knit, line edge to edge.

cut the satin about 1 inch bigger than needed and turn and press 1/2 inch seam allowance before you start to sew.

you can machine stitch (use a zigzag or other stretchy stitch) or hand sew

you can invisible whip stitch or you can use a sharp tapestry (crewel work) needle and sew the lining on using a blanket stitch --this is very visible, but done evenly and neatly, it is very attractive.
use the same yarn you knit with, or pearl cotton, or constrasting yarn.