Each dish and ingredient in osechi has meanings, such as good health, good harvest, happiness, prosperity, long life, and so on. It's said that yellow colored dishes and ingredients such as kazunoko (herring roe) symbolize prosperity and that various beans (mame) imply a wish for good health. Also, red/pink and white colored food, such as pink and white kamaboko (fish cake) slices represent celebration colors.
Traditionally, people finish preparing osechi dishes by New Year's Eve so that they have food for a couple days. Nowadays, many people buy ready-made osechi dishes at stores instead of cooking them at home. It can be time-consuming to cook so many kinds of dishes. It's even possible to order osechi-ryori packed in boxes at department stores, grocery stores, or convenience stores in Japan.