UML is a language. That means it has words and a syntax how to group the words of the language in order to make sentences, paragraphs and finally articles and essays. Like with human languages you can construct anything from blurb to artistic works. And unlike in human languages you use graphical elements like rectangles, ellipses, edges and the like rather than pure alphabet and sentence marks. Learning UML is like learning a foreign language. You first will gain a small set of passive vocabulary which you can increase in practice by stepwise improving your active vocabulary. Talking fluent UML needs quite some practice, but even with some basics you can achieve a lot and will be understood well in the UML community.