I saw a blog post, Stack Overflow Moderator Voting Now Open, saying that users whose reputation reached 250 can vote for moderators, and I want to know who has the privilege to start a moderator election, and how that is done?
The moderators elections only occur when a site needs new moderators. This happens when a current moderator retires, or when the workload for the current moderators get so high that more moderators are needed. The latest method of voting has only been used once. The only people who can start it are
Next time an election is running, users will be notified via a banner on Stack Overflow.
You can see the outcome of the last election here: http://stackoverflow.com/election