First you need to get a license to harvest the energy.
then you have to pay taxes on the expected amount of solar...
Just kidding.
You just need a solar panel. That is a black square made with a meterial that converts the solar energy to electricity. The solar panel will put out current that is usually stored in a battery or connected directly to an electric device.
If you google "solar panels" you will find lots of companies that sell them and you can get specs like how many amps/volts per square foot of surface etc.
There are other, much less common ways to harvest solar energy too.
Some people use black pipes filled with water to get hot water on sunny days (in sunlight things that are black catch the solar energy and get hot).