In a small bowl, mix:
2 tablespoons of plain yogurt, or 1 pack of yogurt starter
2 tablespoons of milk or cream
Stir until it forms a smooth paste.
Add to the Remaining 1.5 quarts of milk or cream.
Mix thoroughly so the culture is evenly distributed.
Pour the yogurt mixture into the glass bowls that come with your Ultimate Yogurt Maker, or the little single serve jars if you bought those instead. If you have the jars and bowls, I suggest culturing the yogurt in the bowls, and then pouring the finished flavored yogurt into the individual jars. It's much easier to flavor the whole batch at the same time.
Seal each one with its lid.