When caucusgoers show up tonight, what will they actually vote for? And how do the caucuses work?

The GOP caucuses don't work like regular elections, in which voters stand in line and file into booths. Nor do they work like Iowa's Democratic caucuses, where voters stand in different areas of a caucus site for head-counting.

The Iowa caucuses will award no delegates to any candidate, and they follow a complicated delegate-selection process. But the Iowa caucuses are significant for two reasons: timing and tradition.

Each of Iowa's 1,774 precinct caucuses can follow its own rules. In and around Des Moines, for instance, some precincts draw hundreds of voters to schools and community centers; in rural areas, handfuls of Republicans will gather, in private homes in a few cases.

The larger caucus sites will work like this: Before the doors open at 8 p.m. E.T., 7 p.m. local time, caucusgoers will line up outside , where campaign supporters and interest-group activists will be able to wave signs, talk to voters and, generally, campaign. At check-in, Democrats and independents will be able to re-register Republican on the spot, meaning that, for practical purposes, Iowa's GOP caucuses are open to anyone who wants to participate.

Many GOP caucus sites will have chairs, or bleachers if the caucus is held in a gym; at others, voters will simply stand around in a room. Temporary caucus chairmen and secretaries will gavel the proceedings open, after which the Pledge of Allegiance will be recited. The caucusgoers will then elect a chair and secretary, usually by voice vote, to officiate for the rest of the evening.

The presidential vote comes first. Candidates or their representatives - sometimes well-known figures from out of state, sometimes local supporters - will be given about two minutes each to deliver speeches. After that, caucuses will hand out "ballots," most often blank slips of paper on which voters write a candidate's name.

Voters will drop their ballots in boxes, or just hand them in; different precincts use different rules, affording different degrees of secrecy. Votes will be tallied, and the caucus chair will announce the winner at that precinct. Caucusgoers can leave after voting for a candidate, and many likely will.

Next, the delegate selection process begins, and here's where Iowa's system gets complicated. Precinct caucuses will elect delegates to March 10 county conventions, which in turn will elect (from their pools of delegate-attendees) delegates to congressional-district conventions and the June 16 state GOP convention, which will in turn elect Iowa's delegates to the Republican National Convention. Votes for county-convention delegates aren't too competitive on caucus night, and more attention is paid to national-delegate selection at the later convention votes.

After voting on county-level party positions and signing up junior delegates, to participate in the Iowa GOP's youth program, caucusgoers can submit platform proposals for the county GOP committees.

And after that, when the Iowa results are reported nationally, presidential candidates will pack up and move onto New Hampshire and South Carolina, leaving Iowa to dominate national political storylines for another week, and not again until 2016.

In 1972, the Democratic Party, the only party engaged in a primary battle that year, moved the date of its Iowa caucuses from the middle of the calendar to the start, scheduling the voting contest in January. Four years later, in 1976, the Republican Party moved its caucuses to January as well, solidifying Iowa's status as the first-in-the-nation vote.

The caucus has a mixed history when it comes to choosing the eventual nominee of both the Republican and Democratic parties. Five Democratic winners - Jimmy Carter, Walter Mondale, Al Gore, John Kerry and Barack Obama - along with three Republican winners - Gerald Ford, Bob Dole and George W. Bush - have parlayed their Iowa victories into Democratic and Republican presidential nominations since 1972.

But where the event truly gains its importance is in terms of momentum. Leading up to the Democratic primary of 1972, Sen. Edmund Muskie of Maine was widely considered to be the front-runner. Muskie received the highest percentage of the vote in Iowa that year, but his challenger, Sen. George McGovern of South Dakota, made a very strong second-place showing. McGovern's second-place finish gave him a boost of media attention, which he rode all the way to his party's nomination.

Prior to 1976, Georgia Gov. Jimmy Carter was little known outside of his home state. His first-place finish among the five Democratic candidates in Iowa brought him into the national spotlight and, like George McGovern before him, took him all the way the Democratic nomination for president.

Many people have criticized the importance placed on the Iowa caucus, arguing that the state is a poor representation of the rest of the country. Indeed, the demographics of the Iowan population differ from the demographics of the country as a whole. Iowa's population is 91.3 percent white, according to the 2010 Census, compared with 72.4 of the U.S. population.

Only 2.9 percent of Iowans are African-American and people of Hispanic or Latino origin make up 5 percent of the state, compared with 12.6 percent and 16.3 percent across the country, respectively, according to the 2010 Census.

But Iowans stand by their caucuses. They are fiercely proud of their state's role in electing presidential candidates and take the task seriously. Retail politicking has long been the key to success in the Hawkeye state. Candidates typically spend months trekking across Iowa's 99 counties, shaking hands, kissing babies and, even sometimes, in the case of Texas Gov. Rick Perry, pulling beards.

That's not to say big money isn't spent on the Iowa caucuses. It's estimated that in 2008 more than $51 million was spent in the state on ads, headquarter rentals, hotels, food, transportation, etc. The candidates have spent more than $2.4 million and counting on ads alone in this election cycle.

Despite Iowa's sizable hype, no national delegates will be directly at stake Jan. 3. In presidential voting, the Iowa GOP caucuses are essentially a statewide straw poll.

The Hawkeye State will send 28 delegates to the Republican National Convention in Tampa Aug. 23, out of 2,286 voting delegates total, but all of Iowa's delegates will be "unbound," or free to vote for any candidate for president or vice president.  Iowa works differently from most states, which will award delegates to presidential candidates proportionally, according to how much of the vote each candidate captures. Most of those delegates will be required to vote for a specific candidate during the first round of voting at the national convention. Iowa's won't.