stick them in a jar of water. break off the green shoots when they are about 3". stick those shoots in another jar of water and root them. when you have some descent roots pot them up and keep them well watered. plant these when they are vines about 10" long. plant 1 set every 18" .
ALWAYS ALWAYS ALWAYS plant sweet potatoes under BLACK plastic - that keeps the runners from setting down roots and making a bunch of tiny sweet pots - you will get nice potatoes that way and they will be clustered around your set like a sun dial - we've gotten them almost as large as a football. you need loose friable soil - a piece of 4 Mil BLACK plastic (LOWES) 10' X 25' ( two of these will give you enough for 36 sets). locate the center line along the length of the plastic sheet - cut 3" squares out for your sets, 18" apart - water them well the first week - 10 days until they are well established. keep the runners ON the plastic. sweet potatoes are tropical - they like to be HOT and they do not like to be too wet. we don't plant them until the last week of May or first week of June and we ALWAYS dig them (very carefully with a fork) in mid September . if the temperature drops below 60 they will go into a sort of hibernation mode. done right 36 sets will give you north of 70 lbs of sweet potatoes