PieCrust websites are highly customizable, but they rely on a few simple principles that you can learn in a minute.
Content sources
A PieCrust website is made of content sources, which are what tells PieCrust where to find content, and how to read it.
In most cases, a content source will read content from more-or-less organized files on disk. Sometimes, that content will be media files (images and animations), or some kind of code (Javascript or CSS related), but most of the time this will be the text you want to publish. As a result, in this documentation, we mostly talk about “page sources” as opposed to the more generic “content sources”.
You can read more on content sources here.
Content pipelines
Once PieCrust knows about your content, it needs to be able to bake it into static files, or to serve it to a browser. That’s what content pipelines are for: they know how to process raw source content, and convert it into whatever the output format is supposed to be.
In some cases, the output format is a web-related format like HTML, RSS/Atom, Javascript, or CSS. In other cases, it might be JPEG, PDF, or anything, really.
You can read more on content pipelines here, especially the two main pipelines in PieCrust, the page and asset pipelines.