The NDS, Houston Landscape and Fairfax County, Virginia, websites all offer diagrams displaying the components you need to install a French drain. The websites also offer step-by-step instructions explaining how to install a French drain.
The NDS website offers the most in-depth explanations about French drains. It explains the common uses of French drains, such as to prevent water from affecting walls, foundations and basements. It also explains how to find the necessary slope for each drain, as well as how to pick and layer the right aggregate. The NDS website offers a calculator that can help you determine the approximate run-off involved for each French drain system.