In short, a patent is a grant of specific property rights for an invention in exchange for full public disclosure of the details of the invention. Patents are typically issued by a government body. In the United states, that body is the United States Patent and Trademark Office (USPTO).
According to the USPTO...
The right conferred by the patent grant is, in the language of the statute and of the grant itself, “the right to exclude others from making, using, offering for sale, or selling” the invention in the United States or “importing” the invention into the United States. What is granted is not the right to make, use, offer for sale, sell or import, but the right to exclude others from making, using, offering for sale, selling or importing the invention. Once a patent is issued, the patentee must enforce the patent without aid of the USPTO.
Because patent documents contain highly technical and oftentimes obfuscating language, it can be difficult to locate relevant patents especially if you do not know the patent number or inventor's / assignee's name. Keyword searching alone will only get you a small part of the full scope of patent documents related to a particular topic. Happily, modern search tools are making it possible to search for patents much more easily.
Keyword searching is probably the most familiar search strategy, since this is typically what we use when searching for other types of documents. Finds patent documents containing the word(s) you entered, and sometimes common variations on those words.
This involves searching for the person who invented the item being patented, or who has been assigned the patent rights. The assignee can be a company, not just a person. The inventor can waive their right to be named in the patent document, so this is not a foolproof method even if you know the inventor's name.
Precision searching using a patent classification system, typically Cooperative Patent Classification scheme (CPC). These systems organize patents hierarchically based on what they are about or for. If you know the classification for the type of item you're interested in, you can quickly locate all patents for that type of item regardless of language used.
Contact your librarian for more help with patent searching. A librarian can help you develop search strategies, navigate a CPC search, and more.
If you are considering patenting an invention and require an absolutely thorough search for existing patents, your best bet would be to get in touch with a patent attorney.
I am a librarian and not a patent attorney. I can help you get started searching for patents. I cannot provide legal advice.