a lot of how the election systems work here in Wisconsin.
To throw a few more curves, in Presidential years there are two partisan primaries, the one in the spring for president and another in the fall for all the other races. As Theshadow mentioned the partisan primary is open to any and all who wish to vote but one thing not indicated was that for the purpose of the ballot you have to declare the party you are voting for. In other words, if you mark the ballot that you are voting Green, only the votes for individual candidates in the Green party primary are counted. By the way, there sometimes are separate ballots for each party.
In non-partisan races, there can be a primary as well. A primary is held if twice as many stand for election than there are seats. For example, if a school board race has two openings and four people file papers then a primary is held. The primary is the third Tuesday in February.
A couple of suggested resources, the Wisconsin Blue Book is one. You can get a copy for most of your state elected officials or look at it at the local library. It has all the formulas for when and how the elections are held, what races are or are not partisan, terms in office and all that stuff. The second resource is the local county party. You can find the contact info for the Democratic Party folks ( and I know I am making an assumption here) at
http://www.wisdems.org and then pick County Parties on the left. I am sure if you let them know you have an interest they will pile so many jobs on you, your head will spin.