Government agencies or patent offices tend to have the most authoritative information on patents in a particular country. They're a good place to look when you need to verify information or are doing research that has legal implications.
Third party resources are also available to help you find patents. They offer specialized search features, and will export citations in a variety of file formats.
Each database operates a little differently. Always read the help documentation provided to make sure you're searching effectively. You can also refer to these guides and tutorials to assist you in your searching:
You can also search for patents by their classification. These resources can help you do that: