Instructions
Search the town for Joan the boar on a Sunday between 6 a.m. and 12 p.m.
Buy a red turnip seed from Joan for 1,000 bells. Only one seed can be purchased each Sunday.
Return to your home, and plant the seed in the desired location.
Water the seed daily. The length of time that the seed is allowed to germinate determines the amount of bells that Tom Nook will pay you for the harvested turnip. This ranges from two to 16,000 bells, so it is definitely in your best interest to allow the seed to grow for six game days.
Select the shovel from your inventory, and use it to harvest the readied turnip.
Take the turnip to Nook, and sell it in exchange for bells.