Question on finishing a knitted jacket

I’m done knitting all the parts of a jacket for my 2 years-old daughter.

In the finishing part, it says to sew the cast off edge of the hood.
Does that mean to sew it with a sewing machine? or just use a piece of yarn and manually sew the 2 edges together with a piece of yarn?

What does seam up mean?
I need to sew in sleeves and seam up underarms

Thank you