photo credit: bettyx1138
Adjectives are tricky little buggers. While usually limited to modifying nouns and pronouns, they sometimes modify other adjectives as part of compound adjectives. These compounds should be hyphenated when they appear before the noun or pronoun they modify, and unhyphenated when they appear after it. For example:
John is a second-rate dancer.
but
As a [...]

It is important to know the eight parts of speech to craft intelligent, and intelligible, sentences. You use them all the time, but if you forget the difference between an adjective and adverb, you wind up coining new usages and infuriating copy editors.