Lexicographers—the people who write dictionary entries—don't make words. Instead, they find them, research their use in the lexicon, and record them in our Dictionary.
When modern lexicographers define words or find words to add to dictionaries, they tend to approach their work from the angle of descriptivism. That is, they observe how the language is being used, and then write definitions based on that research. For examples of our lexicography work, check out our most recent lexicography update: New Words Drop! Get The First Look At Our Fall 2023 Collection Of Dictionary Additions
This does mean that you cannot invent a word and petition to have it instantly admitted into the dictionary. You can invent a word and use it, of course, and if your word catches on, it might end up in the dictionary someday in the future!