The smallest element in a language is a letter. Put several letters together and you can get a syllable. Two or more syllables often form a word. A few words connect to a phrase. A few phrases make up a sentence. If you put a few sentences together, you get a paragraph. A few paragraphs can make up an essay. A few essays form a chapter. A few chapters can make up a book.
In organ improvisation, the smallest unit is of course a note. Putting several notes together makes a motive. Two or more motives form a phrase. A few phrases make up a sentence. If you put a few sentences together, you get a period. A few periods can make up a simple form. A few simple forms can make up a compound form. A few compound forms make up a large-scale form. A few large-scale forms will make up a multi-movement composition.
Isn't this the way we learn to use a language?
One way to improvise on the organ is to tell a story through musical language. But first, you have to learn to connect notes into motives, invent phrases, sentences, periods, simple forms, compound forms, large-scale forms and multi-movement pieces.