Here in Washington we have both a caucus (this Saturday February 9th) and a primary (Tuesday February 19th.) Weird I know! We used to only have a caucus but then in 1988 folks decided they felt left out of the primaries so they voted to add one.
So which should you do? If you're a Republican you can do either (or both.) The republican party splits its nomination delegates between the results of the caucus (49%) and the primary (51%.) And you can participate in both so long as you do both for the same party.
If you're a Democrat you can do both, but there's really no point because 100% of the delegate are allocated according to the caucus. That's right folks, your vote in the primary will make no difference in who gets nominated. (Okay so you could make an argument that the news results from the primary could affect things somehow, but...)
So should you caucus? I say yes. why?
So what do I do on Saturday?
1) find out where to go
-if you're a Democrat go here http://www.wa-democrats.org/caucusfinder and find out where to go
-if you're a Republican contact the party's chapter for your county. A list of the county parties is at www.wsrp.org (King County Republicans have a caucus locator at http://kcgop.org/caucus_locator.html)
2) show up at 1pm on Saturday
3) once there, either go to the corner of your preferred candidate (if you have already decided) or listen as people try to convince you which corner to go to and then make your decision (if you come in undecided)