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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 [...]

Appositives are nouns or noun phrases that represent the same thing and sit next to each other in a sentence. For example,
My wife, Jenny, should know how lucky she is to be married to me.
Here, My wife and Jenny are the same person; Jenny serves to explain my wife.
Apposition is a technical concept. In fact, [...]

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.

Don’t just stick an s at the end of these!

Attorneys general
Courts-martial
Mothers-in-law
Boards of Education
Rights-of-way
Culs-de-sac
Chiefs of Staff
Passers-by
Men-of-war
Heirs apparent
Notaries public.
Runners-up