here is something that can explain it better than I can
How do primaries work?
Most delegates to both the Democratic and Republican national conventions in 2008 will be chosen via state primaries, held from January to June. Those delegates will pick the parties' nominees for president and vice-president.
A presidential primary is much like a regular election: Voters go to polling places or mail in ballots to choose among candidates in a government-run procedure. The voters actually are selecting national convention delegates, who are required to give their support at the convention to the candidate to whom they are pledged, but only the candidates' names appear on the ballots.
The Democrats will award delegates in proportion to the primary vote for a candidate in a state. For example, if 100 delegates are at stake in a state's primary and Hillary Clinton wins 60 percent of the vote, with Barack Obama getting 25 percent and John Edwards 15 percent, Clinton will get 60 delegates, Obama 25 and Edwards 15.
The Republicans don't have that rule and favor winner-take-all primaries. So if Rudy Giuliani wins 51 percent of the vote in a winner-take-all statewide primary, for example, he'll get all that state's convention delegates.
Delegate-selection rules are generally set by the parties and can vary from state to state. Some, mostly smaller states, allot delegates indirectly via caucuses, which are meetings of voters affiliated with one party. Caucuses feed into district and state conventions, and delegate selection is usually less binding than in a primary.
The Iowa caucus, on Jan. 3, is the first event on the nomination
calendar. In Washington state, Democrats will make their initial choices at caucuses Feb. 9, while Republicans will split their process between caucuses on that date and a primary Feb. 19.
Both parties will fill out their conventions with "superdelegates," who are public officials or party officeholders selected by virtue of the positions they hold, and who are not bound to support a particular candidate.
Primaries emerged as a democratic reform in the Progressive era in the early years of the 20th century; Oregon was the first state to enact a primary into law, in 1910.
Primaries waxed and waned in popularity through much of the 20th century: As recently as 1968, the Democrats nominated a presidential candidate, Hubert Humphrey, who did not run in a single primary. Post-1968 reforms have greatly increased the number of primaries.
States have sought to boost their influence in the nominating process by joining in simultaneous regional primaries or by moving their primary date earlier in the year.
The Republican National Committee has voted to strip half the convention delegates from five states that have scheduled primaries before Feb. 5; the Democrats have disqualified all delegates from New Hampshire (Jan. 8 primary) and Florida (Jan. 29 primary).