You don't need database theory. You need to know what you're storing, who it belongs to and what happens when it's missing.
Data is just the list of things your site remembers. A recipe. A birthday. A person. Each one has a few facts attached to it, and that's the whole concept.
Three questions per thing
What facts does it store? Who is allowed to see it? What should happen if a fact is missing?
Answer those three questions for each thing your site remembers and you have written a data model without ever using the phrase.
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