slip stitches onto spare needle then...?

[multhore]

Hi everyone. I'm a returner to knitting and am making a really simple cell phone cover with a pocket.
The instructions say to slip the pocket stitches onto a spare needle. I then have to cast on some more for the main part.
Is it that simple? Do I break the yarn and just leave the stitches to one side until needed?
All help is appreciated.