Read Overview: Zettelkasten Method (zettelkasten.de)

Using a Zettelkasten is about optimizing a workflow of learning and producing knowledge. The products are texts, mostly. The categories we find fit the process well at the moment are the following:

Knowledge Management: general information about what it means to work and learn efficiently.
Writing: posts on the production of lasting knowledge, and about sharing it with others through your own texts.
Reading: posts about the process of acquisition of new things and the organization of sources.