Put stitches on holder, break thread or not?

I am making the Eloise cardigan on the Lion Brand website; my first attempt at a knitted baby sweater. I am confused by the directions…it is knitted back and forth on a circular needle. I have knitted the back up to the sleeves and it says to place the stitches on a holder. Now I am supposed to start the left front and it says to cast on 29. I don’t know if I’m supposed to cut the yarn or not? If I don’t cut the yarn, how do you cast on? Later in the pattern you are to place the sleeves, back, fronts on the circular needle and knit, combining all the pieces. I understand the concept, just am stuck about whether or not to cut the yarn for all these separate pieces. Thanks in advance from this novice knitter. I’m an accomplished crocheter, but really want to master knitting!!

Yes, you should cut the yarn, leaving about a 6 inch tail which will be woven in later. The same will go for the sleeves and at least one of the fronts. Possibly you can continue with the yarn attached to the right front, but the other pieces will all be separate.
It will be great to combine knitting and crochet. Good luck with the sweater!