A patent is a property right granted by a government agency (in the United States, it's the US Patent & Trademark Office) for a novel, useful, and non-obvious invention. Patent protection lasts twenty years from the filing date and allows the inventor or their assignee to exclude other people from making, using, selling, or importing an invention.
Patents are excellent sources of technical, legal, historical, and commercial information. You might want to search patents because . . .
Patents can be difficult to search because they often use complicated, obscure legal-technical language.
The right way to do a patent search depends on what you're trying to find and how rigorous you need to be. A basic exploratory search might take the form of a keyword search in a database like Google Patents or Derwent Innovations Index, using patent classifications to expand or narrow your search as needed. A more rigorous patentability search, on the other hand, might follow the USPTO's official "Seven Step Strategy" process and use the official government patent searching tools.