We can also use the preposition "de" to express the material of which something is made. A preposition is necessary when we do this in English, but we must use "de" when we talk about what something is made of Spanish.
For example:
"la puente de madera" (the bridge of wood, the wooden bridge);
"el cuaderno de cuero" (the notebook of leather, the leather notebook).
This usage has also extended to signify the matter or issue of something.
For example:
"el libro de geografía" (the book of geography, the geography book);
"hablábamos de la política" (we were talking of politics, we were talking about politics).
This same usage is also used to express the nature, condition, or character of a person. For example: "es un estudiante de talento" (he is a student of talent, he is a talented student).