the sun is source of energy?

The sun powers photosynthesis, which allows grass, flowers, and other "primary producers" to grow. These producers are eaten by "primary consumers" such as rabbits and mice. These are eaten by "secondary consumers" as hawks and snakes. Some of these are eaten by "tertiary consumers" such as humans and wolves. If the grass dies, the whole chain will die.

The sun also warms the planet, as temperature is a measure of energy.

Yes, and the source for all life on Earth as we know it

yes

yes, in the form of electromagnetic radiation