Nowadays, applications in free software world are more and more intuitive. Even usability teams exist to help developers achieve a friendly and easy user interface. Basic usage of most applications can be learnt quickly, usually just through experimentation and "first line" help, such as tooltips.

But mastering an application is a very different question. In order to unleash all the power an app can provide, you'll likely need to read its documentation, manuals... Of course, reading documentation can also be used to learn the basic usage of an application, although most people just open an application and explore by themselves to learn that.

A reason for this can be that those information sources are commonly centered on "what can be done" instead of "how something can be done". The answer to "how something can be done" is usually found in tutorials and, of course, how-tos.