A how-to is an informal, often short, description of how to accomplish a specific task. A how-to is usually meant to help non-experts, may leave out details that are only important to experts, and may also be greatly simplified from an overall discussion of the topic.
One of the earliest how-to books was published in 1569 and entitled, A booke of the arte and maner, how to plant and graffe all sortes of trees: With divers other new practise, by one of the Abbey of Saint Vincent in Fraunce by Leonard Mascall.
A similar concept can be seen in many of the [topic] For Dummies series of tutorials and also in many other introductory surveys entitled with the suffix "101" (based on academic numberings of entry-level courses).
Usage in the world of computers
It is common practice to write the phrase as "HOWTO" in the open-source community. This is consistent with the traditional naming scheme for technical documentation, such as FAQ and README. Another possible reason is that this makes it easier to find a how-to in search engines like Google as searching with the words "to" and "how" does not necessarily deliver relevant search results.
In the beginning, most how-tos on the Internet were the result of a complex process in which an author wrote a how-to for potential readers. After 2001, user added content played a more and more important role on the internet in a trend that is widely referred to as Web 2.0. This had a profound impact on the way in which how-tos are generated on the internet, as the readers and users were able to add to and improve the on-line content.