Help, what does it mean to sew 2 crochet pieces together?

[sep335]

Working on a one piece baby kimono. This works up so quickly, almost done..and just started 2 days ago. I think I will use this for some donation work. I love a quick small easy pattern. But my question is...how do you sew together crochet??? The pattern says to sew together seams underarm sleeve and sides. I have never made crochet garments before. Do I sew with thread and needle, sewing machine or do they mean to join seams with a running yarn...just wondering...I would think you can't really "sew" crochet. but what do I know! Thank you for sharing your expertise with this newbie. Can't wait to post a picture. Funny thing, I don't even know any babies to give it to.