There are many differences between butterflies, flamingos, and tigers, but one thing they all have in common is that they are all consumers. In ecosystems around the world, there is a pattern of relationships between organisms within that ecosystem.
The main role of a primary consumer is to facilitate the transfer of energy through the food chain. Primary consumers do this by eating plants to gain energy, and then are available as a food source for other consumers in the ecosystem. It is helpful to use food webs and food chains when trying to understand the role of a primary consumer.