Answer:
Primary Election: This is where people get to decide their preference for their party's candidate, or a candidate in general.
Runoff Elections: These election are only done if their is a tie, or in (A certain state. ex. Georgia) Get's less than 50% of the votes. During these elections ONLY 2 people can be voted in.
General Elections: This is after all candidates has been picked in the Primary, and now it's time to vote, for the person you want IN office, it's basically the real election (Presidential, House, Senate, Governor, Mayor, and so much more)
Special Election: This is usually started by the Governor, but can be done are usually done for the purpose of filling a vacant seat.