When someone mentions "solar power" I think the majority of people instantly think of standard solar (photovoltaic) panels, which convert light directly into usable electricity. But "solar power" and "solar energy" are much more broad than that, including any system that uses the sun as a source of energy.
So, if you're not converting the light to electricity, how is it usable? By converting the light to heat. Creating an efficient photovoltaic panel would be a do-it-yourselfer's nightmare, including the cost of materials as well as the hazardous materials needed and the labor involved. But harnessing the energy of the sun in heat form is as easy as putting something dark in the sunlight.
The basics are simple, something dark in direct sunlight will heat up and can be used as a solar collector in a solar energy system. After that, creativity, research, and trial and error are key.
To increase efficiency, reflective materials like mirrors or foil can be used to focus more light onto the solar collector. Tracking systems can also be used to aim the collector or reflector systems to more efficiently collect light as the position of the sun changes.
As an example, a basic solar energy system could consist of an enclosure with a black piece of metal collecting sunlight and a series of pipes behind it. These pipes could contain water or air, which would be heated as the metal in front of them heated up. Heated air could be pumped directly into a building (during cold weather), and heated water could be directed to the intake of a conventional water heater (saving electricity or gas by preheating the water and taking that workload off of the water heater itself).
Once again, imagination and creativity are important. You can find examples of homemade solar projects like this all over the internet, some even more basic – maybe just a wooden frame painted black inside, with a sheet of glass over the front to let light in and keep in the collected heat. It's something that almost anyone can experiment with.