Hi all! A friend just directed me to this site with a question she couldn't answer for me

I'm hoping someone here can help
I purchased a book for knitting slippers today. When I sat down to get started I realized that the first thing it says is that "slipper is worked with two strands held together". I'm a new knitter...as in, I can knit a dishcloth and that's it! LOL! Because of that, I need baby steps
Thanks!
MamaJo