HOWTOs are detailed reference documents on a specific subject, usually following a step-by-step approach. A HOWTO is a good document to help you discover a task or a topic you don't know. It will provide you with the basic steps and the major references.
These documents are particularly useful when you decide to provide or access a new service with your Linux system, or when you embark on a technically complex project. For example, you may have the option of accessing the 'net with a DSL or Cable Modem service - excellent guides are available in the form of HOWTOs.
Authors of these documents often include references and links to sites that they have found useful. You may find the information you need at one of these hyperlinked sites rather than in the HOWTO itself.
To find HOWTOs, the first place to go is the Linux Documentation Project (LDP). The LDP includes a HOWTO Index Page that I suggest you bookmark in your browser.
These HOWTOs are written by Linux users and are periodically updated by the authors. Many authors provide the latest version at a personal website and a hyperlink to the latter is typically provided in the document. This version may be newer than the one available at the LDP website.
Note also that other HOWTOs are available, the authors of which have not submitted them to the LDP. It is definitely worthwhile trying to find these with an Internet search engine, using the "howto" keyword.