The potatoes you use can come from the grocery store, be purchased online or found at nurseries as seed potatoes. Sometimes grocery potatoes are sprayed to prevent them from producing "eyes" the buds of green growth. On the other hand, I checked my bag of red potatoes in my closet and found some that were budding. I also bought some varieties from a local home improvement store.
You don't necessarily need your potatoes to have stalk eyes or signs of growing before you plant them. But it does add a bit of comfort knowing they have starting growth when you plant them. You can sit your potatoes in a bowl and wait for them to start growth if you wish before planting.
These red potatoes came out of a gourmet bag of potatoes I bought. You can see the eyes of the potatoes have buds. (click the photos to enlarge them)
The five gallon bucket is planted the same way. It was an upside down tomato bucket.