After a year of debates, bus tours, gaffes, town halls, tweets, electrifying rallies, and baby kisses, the presidential primary process is finally getting underway. Over the next several months the large field of candidates will shrink, and we will ultimately be left with two nominees ready to lead their respective party to victory in November.

How do we go from many to two?

The presidential candidate nominating process is a drawn-out, convoluted affair, so we’re going to try to take out some of the confusion:

The delegates decide

First, it’s important to note that candidates aren’t directly elected by voters—rather, the votes determine the numbers of delegates a candidate gets at the party’s national convention.

The parties’ national conventions happen once every four years, in the summer before the general election. Throughout the nominating process, candidates pick up delegates state-by-state, based on how many votes they get in each state. The rules are different for each party: Democrats get delegates based on proportional representation rules, while the Republican Party gives more discretion to states in deciding delegate-allocation methods.Obama-Accepts-Nomination--009

At the end of the day, candidates need to send a lot of delegates to their parties’ conventions to have a hope of being the nominee. For example, on the Republican side, there will be around 2,470 delegates sent to the convention this summer—and a candidate needs at least 1,236 to win. That’s why the crowded GOP field makes it so unlikely that lower-tier candidates will become their party’s nominee.

Primary, caucus…who cares?

You’ve probably heard the word “Iowa” on the national news more times in January than you will for every other month in the next four years combined. Why?

It’s pretty simple: Who wins—or comes close—in the first few states has a significant impact on who will become a party’s nominee. Here’s a stark example: Since 1976, every single party nominee has won either Iowa or New Hampshire (with the exception of Bill Clinton in 1992). And when several states vote on the same day on Super Tuesday – several are population-dense, delegate-rich states – a poor performance can doom even a once-dominant candidate.

How many ways can a state pick delegates?

The short answer is two, with modifications.

Let’s start with the caucus, since Iowa’s first up. Caucuses are unconventional events run by the state’s political parties (as opposed to by the state government). The parties host private events where their members get together and figure out whom to vote for. On the Republican side, voters gather at sites across the state, hear speeches from candidates’ representatives (or even the candidates themselves), and then voters write down whom they support and hand in their ballots.

For Democrats, voters gather at voting sites. Then they separate into groups based on whom they support, and numbers in each group are counted. If one candidate’s group represents less than 15% of total voters, then those voters are released, and from there it’s a mad dash from the surviving candidates’ supporters to convince these free-floaters to join their tribe.

Here’s an example of something that could easily happen today: if Martin O’Malley supporters don’t make up 15% of voters in any caucus site in Iowa, Sanders and Clinton supporters will scramble to get the free-for-all O’Malley voters onto their respective teams.

Primaries are a good deal more straightforward: You stand in line, step into a private booth, press some buttons or fill out a paper ballot, and cast your ballot. The fine print is that some states have closed primaries, others are open, and others still are semi-open or semi-closed.

In a closed primary, you have to be registered with that party to vote in its primary—you want to vote for Hillary Clinton in New York? You’d better be registered as a Democrat. If the primary’s open, party registration doesn’t matter, so a registered Republican could vote for Bernie Sanders, and an Independent could vote for anyone. In semi-closed and –open contests, the basic rules usually apply, with tweaks and often more state-party discretion in determining voting rules.