As a developer, you will undoubtedly work with sensitive information such as passwords. How you handle this information during development is very important. In the past, I have received copies of a client's live database to use for testing. This does pose a very real security risk for your client.
Often, we keep settings in a web.config file (when working with web applications). For this example, though, I will be demonstrating a console application that uses an App.config file. The same logic can be applied to a web.config file too.