If you want to talk about something in general, when do you put an article in front of it and when do you not?
For example how do you say "I like apples. Apples are important" or "Trees are important" or "Man is the only conscious animal" ? Thanks you.
The answer you need is here in this
Span¡shD!ct Reference Article.
In particular, see these notes on the Reference Page:
When NOT to use definite articles
1. With titles when addressing a person, or with San, Santo/a, Don, and Doña Señora Ocón,
¿cómo está? (Mrs. Ocón, how are you?)
Santo Domingo está en el caribe.* (Santo Domingo is in the Caribbean.)*
Don Juan es un hombre muy romántico. (Don Juan is a very romantic man.)
2. With nouns referring to academic subjects
Mi amigo estudia matemáticas y biología.* (My friend studies math and biology.)*
3. With ordinal numbers in titles
Felipe II (Segundo)* (Philip the Second)*