The potatoes are ready to plant after chitting for a few weeks on a warm windowsill.
As you can see in the picture, there are tiny shoots growing out of the potato ready to create new growth. This growth will establish new roots in the soil and create potatoes.
You do not have to chit potatoes for them to grow well but it is possible to gain quite a bit of growing time early in the season. I will have gained at least 3 weeks of the growing season by doing this and be able to harvest my potatoes much earlier.
In January or early February, I place my seed potatoes on a sunny surface and leave them to chit for a few weeks. Then, usually around Good Friday, I plant the chitted potatoes in buckets and put them in the greenhouse initially and then after a few weeks they can be taken out into the garden. In about 12-16 weeks, we will have a lovely harvest of potatoes from the garden ready for Sunday Dinner.