How would I explain primary election to 5th graders

A primary election is the process by which voters, either the general public (open primary) or members of a political party (closed primary), can indicate their preference for a candidate in an upcoming general election or by-election, thus narrowing the field of candidates ... In a primary election, registered voters may participate in choosing the candidate for the party's nomination by voting through secret ballot, as in a general election. There are two main types of primaries, closed or open, that determine who is eligible to vote in the primary.