When to use "de" on describing?
Uh people, I have this confusion wherein I do not know if I should use "de" on describing such as "Una clase de Espanol.". I got confused like why not "Una clase espanol."?
"De" has a ton of uses in Spanish: http://www.wordreference.com/es/en/translation.asp?spen=de
In "una clase de español" you use the "de" to indicate the purpose of the class.
Without the "de" you would be describing the class and saying that the class itself is Spanish - as if you were saying it's a big class, it's a small class, it's a difficult class. Spanish does not describe the class itself; it's the purpose of the class.
Español can be either a noun or an adjective.
If it's an adjective, you have to match the gender and number of the noun it's modifying:
Una clase española: "el estudiante tipo de una clase española no suele preguntar"
Unas clases españolas "También estuvimos en unas clases españolas y pudimos probar como se estudia en España."
Las clases españolas: "La realidad virtual llega a las clases españolas para quedarse."
If español is treated as a noun (doesn't change to match the gender number of the other noun), then you need the preposition to show the relationship between the two nouns. La clase de español.
"¿A qué hora termina la clase de español? La clase española termina a las siete y veinticinco de la noche."
For a class of people studying Spanish, I've usually heard "una clase de español." Las clases españolas could also mean classes in Spain.
In this case, "de" shows possession. "Una clase de Espanol" would be translated as "A class of Spanish," or, "A Spanish class." It's easier to understand with people; "Una ropa de rey" means "The clothes of the king," "The clothes belonging to the king," or "The king's clothes." Usually, "de" can simply be translated as "of." I think that in your sentence "Espanol" is part of the noun. An adjective works differently, "Una clase grande." (The big class.) You would not use "de" there, because "the class of big" doesn't make any sense.
The problem is actually with English. We use nouns as adjectives all the time: car seat, math test, etc. Spanish does not allow this, so one must consider how to say what needs saying without using a noun as an adjective: math test = a test of (ability with) math > un exámen de matemáticas.