buen y bueno
when do i use buen and bueno?
Buen and bueno are the same adjective. The only difference is where they are placed (their location and the context).
Buen is used instead of bueno before masculine singular nouns.
For example, Un buen hombre. (a good man) But, una buena mujer. (a good woman). Hombre is a masculine singular noun. Mujer is singular, but feminine. Notice that you would say something like unos hombres buenos if it were plural for men, and unas mujeres buenas for plural women.
The same thing happens with grande, except since grande has no feminine or masculine connotations, you can use it with all singular nouns. Un gran dia. Un/una gran artista. So on and so forth.
Does that answer your question?
"Buen" comes immediately before a noun, "bueno" comes elsewhere. For example:
Un buen hombre ("buen" is followed by the noun it describes)
Mi buen amigo
El hombre es bueno.
Note that this only works for singular masculine nouns. For feminine and plural, the form does not change according to position: "La mujer es buena" remains "Una buena mujer"