What is a patent?
A patent is a legal right granted by the government to the inventor of an invention, which allows that inventor to prevent others from using the invention (in other words, the patent owner has a monopoly over his invention). Specifically, for a limited amount of time (currently 14 or 20 years, depending on the type of patent), nobody can make, use or sell the invention within the United States without the patent holder’s permission. After that limited amount of time, the patent passes into the public domain.
But because an inventor gets this monopolizing right, he is required to fully disclose information about how to make and use the invention. The actual paper patent includes this information, and once it is issued, the patent is publicly available so that the public can access and learn from it.
For example, suppose you get a patent for a doohickey. For 20 years, nobody else in the United States can make or sell doohickey’s without your permission. However, anyone can find out how to make and use the doohickey because the patent itself will be made available by the government.