Light, heat, nutrients, water, oxygen, carbon-dioxide and space are all factors which plants and animals would compete for. In a rain forest, plants compete for light and carbon-dioxide. In winter, birds compete for the scarce numbers of berries and fruit. Plants growing close to a conifer hedge would struggle to survive because they would compete with the conifer for water, nutrients and light. Plants compete for water, light and nutrients.
Animals usually compete for food.
The aim is to survive. The animal or plant which is best adapted will survive. Here is a hedge at the edge of a field of genetically identical wheat plants. The table shows the size of the wheat plants as they get further away from the hedge. Here is a map of a field.