Making offerings at an altar, in a monastery or at a sacred site is a way to help the practitioner remember what is most important in life. Various branches of Buddhism have differing practices and explanations for those practices, but the underlying intent to focus the mind is the same. A typical description of the symbolism of offerings is:
Lighting a candle or butter lamp represents the light of wisdom scattering the darkness of ignorance. Burning incense reminds the practitioner of the fragrance of right behavior. Flowers represent the physical manifestations of Buddha, and food and water represent the nourishing aspect of the dharma (the path to enlightenment).