(Editor’s note: I’m using content within my own “slip box” to write this.)
Start out by forgetting zettelkasten exist. Instead read about what a commonplace book is and how that (simpler) form of note taking works. This short article outlined as a class assignment is a fascinating way to start and has some illustrative examples: https://www.academia.edu/35101285/Creating_a_Commonplace_Book_CPB_. If you’re a writer, researcher, or journalist, perhaps Steven Johnson’s perspective may be interesting to you instead: https://stevenberlinjohnson.com/the-glass-box-and-the-commonplace-book-639b16c4f3bb
The general idea is to collect interesting passages, quotes, and ideas as you read. Keep them in a notebook and call it your commonplace book. If you like call these your “fleeting notes” as some do.
As you do this, start building an index of subject headings for your ideas, perhaps using John Locke’s method (see this for some history and a synopsis: https://publicdomainreview.org/collection/john-lockes-method-for-common-place-books-1685).
Once you’ve got this, you’ve really mastered the majority of what a zettelkasten is and have a powerful tool at your disposal. If you feel it’s useful to you, you can add a few more tools and variations to your set up.
Next instead of keeping the ideas in a notebook, put them on index cards so that they’re easier to sort through, move around, and re-arrange. This particularly useful if you want to use them to create an outline of your ideas for writing something with them. Once you’ve got index cards (slips) with ideas on them in a box, you now literally meet the minimum requirements of a zettelkasten (German for “slip box”, though in practice many will have their ideas in a metaphorical slip box using a digital note taking tool.
Next, maybe keep some index cards that have the references and bibliographies from which your excerpting and note taking comes from. Link these bibliographical cards to the cards with your content.
As you go through your notes, ideas, and excerpts, maybe you want to further refine them? Write them out in your own words. Improve their clarity, so that when you go to re-use them, you can simply “excerpt” material you’ve already written for yourself and you’re not plagiarizing others. You can call these improved notes, as some do either “permanent notes” or “evergreen notes”.
Perhaps you’re looking for more creativity, serendipity, and organic surprise in your system? Next you can link individual notes together. In a paper system you can do this by following one note with another or writing addresses on each card and using that addressing system to link them, but in a digital environment you can link one note to many multiple others that are related. If you’re not sure where to start here, look back to your subject headings and pull out cards related to broad categories. Some things will obviously fit more closely than others, so be more selective and only link ideas that are more intimately connected than just the subject heading you’ve used.
Now when you want to write or create something new on a particular topic, ask your slip box a question and attempt to answer it by consulting your index. Find cards related to the topic, pull out those and place them in a useful order to create an outline perhaps using the cross links that already exist. (You’ve done that linking work as you went, so why not use it to make things easier now?) Copy the contents into a document and begin editing.
Beyond the first few steps, you’re really just creating additional complexity to a system to increase the combinatorial complexity of juxtaposed ideas that you could potentially pull back out of your system for writing more interesting text and generating new ideas. Some people may neither want nor need this sort of complexity in their working lives. If you don’t need it, then just keep a simple commonplace book (or commonplace card file) to remind you of the interesting ideas and inspirations you’ve seen and could potentially reuse throughout your life.
The benefit of this method is that beyond creating your index, you’ll always have something useful even if you abandon things later on and quit refining it. If you do go all the way, concentrate on writing out just two short solid ideas every day (Luhmann averaged about 6 per day and Roland Barthes averaged 1 and change). Do it until you have between 500 and 1000 cards (based on some surveys and anecdotal evidence), and you should begin seeing some serendipitous and intriguing results as you use your system for your writing.
We should acknowledge that that (visual) artists and musicians might also keep commonplaces and zettelkasten. As an example, Eminem keeps a zettelkasten, though he calls his “stacking ammo”, but it is so minimal that it is literally just a box and slips of paper with no apparent organization beyond this. If this fits your style and you don’t get any value out of having cards with locators like 3a4b/65m1, then don’t do that (for you) useless make-work. Make sure your system is working for you and you’re not working for your system.
Sadly, it’s generally difficult to find a single blog post that can accurately define what a zettelkasten is, how it’s structured, how it works, and why one would want one much less what one should expect from it. Sönke Ahrens does a reasonably good job, but his explanation is an entire book. Hopefully this distillation will get you moving in a positive direction for having a useful daily practice, but without an excessive amount of work and perhaps a bit less cognitive dissonance. Once you’ve been at it a while, then start looking at Ahrens and others to refine things for your personal preferences and creative needs.