Cro-knit Double Ended Crochet Hook

I was unpacking things from storage and ran across a double-ended crochet hook. Now I know I have a book on it and tried it in the past and couldn't figure it out for anything.  But I figured I could try again if I could find a tutorial on You-tube and now I am happily making something which may turn out to be a hat. The written directions that came with the hook said to cast on 36 to make a scarf, so I did. But this thing is way too wide to be a scarf, so I thought I'd either make an envelope hat or a vest. Before I make a vest I need to figure out how to make increases and decreases, so I can make arm holes.