The sun supplies all the energy used by living things on this earth. Either directly for the autotrophs or indirectly for the heterotrophs.
Few organisms, such as chemotrophs, bypass this system.
Why in our life is sunlight very important?
We can't live without the sunlight, it's natural that we need it. Because it make us warm in the cold weather, healthy, energy etc. So it's very important for us to have it, and it's like our heart as well.