Light is still a form of energy. There are other forms, such as heat or electrical power, and these can be converted from one to another.

For example, you could use big mirrors to focus sunlight onto a pot of water to boil the water (heat). You could then use the steam to turn a turbine, which turns a generator, which produces electricity. This particular method is not very efficient because some energy is lost at each step along the way.It's more efficient to generate the electricity directly from light.

Electricity or electrical power is basically just the flow of small particles called electrons. So we want to use light to move electrons. How do we do that? When light strikes an atom, it can excite one of the atom's electrons to a higher energy state. (It has absorbed energy.) In most materials, the electron would just fall back down to its original state and give back the energy it absorbed, and give off light or heat. But solar cells are made with a special material where excited electrons get pushed away from the atoms they're excited from. You can tap the energy of all these excited electrons.

An analogy might be to think about marbles rolling down a track into a bowl. You could lift a marble from the bowl to the top of the track (add energy). If the marble falls straight back into the bowl, no useful work is done. But if it rolls down the track, it could turn a little paddle-wheel and do useful work for you. In this analogy, marbles are moved by gravity. In the case of electrons, they are moved by the attraction to positively-charged atoms, and we call this attraction an electric field.

Many kinds of light will work, as you know if you've used a "solar" calculator. Light from the sun (solar power) happens to be very bright, and most important, it's free.