Jeopardy! (the exclamation point is a part of the title) is a half hour long (commercials included) and airs an episode six days per week (occasionally less due to special programming changes). The game consists of three contestants being presented with an electronic board full of "answers" (or clues) to which they must present a "question." It might sound odd at first, so here's an example of how this works:
Contestant #1: I'll take Chia Pets for 200, Alex.
Alex Trebek: The answer is: This is the infamous jingle associated with Chia Pets.
Contestant #2 presses a little button before anyone else, signalling that he/she wants to provide the question.
Alex Trebek: Stacy.
Contestant #2: What is ch-ch-ch-chia?
Alex Trebek: Correct.
The contestants must respond in the form of a question. Had Contestant #2 in the above example responded simply "ch-ch-ch-chia" rather than "what is ch-ch-ch-chia," the response would have been incorrect. The answers available to choose from are organised into six columns according to category (in the above example, the category was Chia Pets) and five rows based on the amount that must be wagered.
Jeopardy! consists of three rounds: Jeopardy!; Double Jeopardy!; and Final Jeopardy!. In the Jeopardy! round, the amounts that can be wagered on a clue in any one category are $200, $400, $600, $800, and $1000. In Double Jeopardy!, these amounts are doubled and the clues are harder. The actual clues themselves are not seen until chosen, only the dollar amount they are worth. Both of these rounds have a time limit and will end when that limit is up, even if there are still unanswered clues on the board. Final Jeopardy! consists of one category with one clue. At the start of Final Jeopardy!, contestants are given the category but not the clue. At this point, they make a wager of their choosing, though the amount cannot be greater than the amount of money each one has already won. The show usually goes to commercials at this point and when it comes back presents the contestants with the clue. Instead of having to reply quicker than any other contestants to this clue, each one must write his/her answer down within 30 seconds. When the 30 seconds are up, anyone with the correct answer is awarded the money they wagered (and anyone with the wrong answer has the same amount taken away from their winnings).
Answering (or "questioning") a clue incorrectly will incur a penalty of whatever amount was wagered to the contestant's score. If Contestant #2 in the above example had answered incorrectly, his/her score would have had $200 deducted. In some cases, these leads to contestants occasionally having negative scores. If a contestant has a negative score at the end of Double Jeopardy!, he/she may not continue on to Final Jeopardy! Contestants don't have to pay anyone if they end with a negative score. In the first two rounds, daily doubles are possible. These are special clues which seem like any other clue until they are chosen, at which point some excited laser-like sound effects play and Alex Trebek lets everyone know what's up. A daily double is like Final Jeopardy! for whoever picks it: He/She can wager whatever amount, so long as it isn't higher than his/her current winnings and only that contestant can respond. If their earnings are below $500, however, they are allowed to wager up to $500 on the daily double.
Jeopardy!'s contestants are usually anyone who has made it through their pre-show questioning try-outs, though occasionally there are episodes where the contestants are only college students or celebrities playing for charity. In the case of the former exception, the clues are usually a bit easier but not that much. In the case of the latter, the clues are much easier as not only are the celebrities playing for charity but not every celebrity is all that knowledgable with regards to Jeopardy!'s usual type of content. Every once in a while there's an episode with teenagers, with clues that are pretty easy compared to the usual ones.
Saturday Night Live has taken to making a parody of celebrity Jeopardy! every now and then with extremely humourous results. The celebrities playing are always portrayed as unbelievable stupid, missing answers that are either outright obvious (e.g. "Name this continent: Asia.") or consist of movies each parodised celebrity was in. This is especially funny when a SNL cast member portrays Sean Connery, who always seems to read the categories incorrectly (e.g. "I'll take the rapists for 100, Alex." "That's therapists." / "I have to ask you about the penis mightier." "What?! No, no Mr. Connery. That's 'the pen is mighier.'" "Dussy it up however you like, Trebek, what I want to know is does it work?").
Unlike more recent quiz shows like Who Wants to be a Millionaire? whose questions are usually more along the lines of random trivia, Jeopardy!'s clues are pretty tough and geared more towards formally educated contestants. Chia Pets wouldn't be a category on a real game of Jeopardy!