how to slip stitches onto spare yarn?

[Jennifer K]

I am knitting a baby hoodie. I am knitting the back. My pattern reads: slip all stitches onto spare yarn. I have still to do the front and sleeves. I still have alot of yarn left in my ball. How do I slip my stiches onto the spare yarn, disconnect the yarn, knit the other pieces, and reattact the yarn to the stitches, without damaging the last stitch I knit? (The stitches I slip will be the hood.)