PieCrust websites are highly customizable, but they rely on a few simple principles that you can learn in a minute.
A PieCrust website is made of content sources, which are what tells PieCrust where to find content, and how to read it.
You can read more on content sources here.
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.
You can read more on content pipelines here, especially the two main pipelines in PieCrust, the page and asset pipelines.