Patents cover inventions and specially how an invention works.
To apply for a patent, it must be: new, something that can be used or made, and innovative.
Patents are difficult to get as lawyers must ensure that a patent is not derivative or is something that already exists - this can take up to five years. When applying for a patent how the invention work must be documented and publicly available for anyone to view. Even though publicly viewable, no one other than the patent owner can legally use the invention unless it is licenced or sold.
Once a patent expires anyone may use the invention and make money from it. Patents last for a maxium of 20 years, and the owner may need to renew the patent every 5 years to continue to exclusivly use / sell their invention.
Some people argue that patents stifle innovation by preventing others using new inventions.