Grammar: A word to strike fear into the heart of the average American. (Or joy, but those rare people are called English teachers or copy editors.) For good or ill, we all know we're judged on our grammar. People believe they can learn a lot about your background, your education and even your intellect by whether or not you have a good grasp of grammar.
Though some people use "good grammar" as a catchall term for "good English," there's more to it than that. In writing, your spelling, punctuation and correct capitalization all count. And whether you're speaking or writing, correct word usage counts too. The best example of this is the ongoing culture war over the word "literally," which has come to mean its opposite, "figuratively." For example, "My roommate literally went insane over the cap being left off the toothpaste." (We certainly hope not!) Some dictionaries have given up and accepted the use of "literally" as "figuratively."
But today, our White Whale is grammar: the parts of speech, subject-verb agreement and verb tenses, voices and moods, and so on. (Words have moods? Who knew?) The questions will start fairly basic but get harder as you go on. So summon your inner Conan the Grammarian, and let's do this!