So here it is:
First, the simple version: Proportional Representation. Each qualified party (last election there were 7 in California) has a primary in which the party's candidates are ranked. All the Representatives for the state are being determined at the same time. If the Green Party gets 11% of the Proportional votes, approximately 11% of the Representatives will be chosen from their top ranked candidates (probably the top 4 candidates). If the Libertarian Party gets 17% they might get their top 7 candidates in. (I believe this is called party list proportional representation.
Second, the feature of Party Seats. Let's say that 10 of the 53 Representative seats are Party Seats. The top 10 political parties as determined by state membership each get one of these seats. Which would mean 7 seats currently filled this way in California.
