How does the cow get energy from the sunlight?

The answer is complex and rather surprising. The plants get their energy to grow from the Sun, they use photosynthesis to trap the energy in sunlight to make sugars (out of water and Carbon Dioxide from the air) which then go into the making of the plants leaves and stems.

Cow graze on these leaves and stems but they can not use the energy in them directly. They chew them up and then pass the ground up bits into a special stomach (cows have 4 stomachs) where microorganisms break down this material and multiply on this food as they do so.

The cow then passes the fermented broth into others of its stomachs where it digests the microorganisms, incorporating their nutrients into its body.

Thus the energy a cow gets comes intally from the Sun, which is stored by plants, which is then used by microorganisms which is then used by the cow.

If you were then to eat the cow then the energy enabling you to move would have come from the Sun.