When an annual plant sprouts from a seed the root grows down into the soil and the shoot grows up into the light. When the bulb of a perennial plant becomes active in the spring it sends out roots deeper into the soil and a shoot into the air. The stem is the part of the shoot that conducts water up the shoot and dissolved food to all other parts of the plant. It supports the other parts of the shoot. The leaves make the food and the flowers enable the plant to reproduce.
Many plants produce shoots that lasts for just one growing season then die in the autumn. Woody plants have a shoot which does not die back but grows new shoots on its branches every year.