Plants are called producers due to their ability to create complex biological compounds like glucose by processing carbon dioxide, sunlight and water. Plants also produce oxygen, contributing the atmosphere that all animals breathe. Producers are found at the base of every ecosystem in the world, providing the foundation of most complex life in the world.
Plants are also called "primary producers," meaning that they are the only living things in the food chain to produce the energy that all animals eventually process. Similarly, primary consumers are known as herbivores, acting as the second link in the chain, and secondary consumers are those carnivores that subsist solely off of herbivores. Tertiary consumers are predators that eat both herbivores and carnivores. Humans can be considered tertiary consumers, for instance.
There are some plants that are consumers. For instance, the Venus' fly trap and similar plants have mechanisms to trap and digest insects and small animals to get the nutrients they need to grow and survive. Venus' fly traps are still plants, however, and gather some of their nutrients from gases and the soil they are rooted in. Plants such as these are found in areas with poor soil quality, forcing them to capture small prey to supply their missing nutritional needs.