Here is an example of "because" used correctly in a sentence: "I don't like rodents, because they always bite me." The words "for and "as" are sometimes used instead of "because", the use of "for" is mostly limited to 18th century authors, while "as"(in the stead of because) is used by both antiquated and contemporary authors. Both these things are generally only seen in writing, I have never heard someone use "as" instead of "because" in conversation. Examples: "I detest rodents, for they always bite me." "I don't rodents, as they always bite me."

It is hard to answer without more context but both "for" and "because" can be used as prepositions. ".......because of......." or "....for these reasons......"