Basically, the federal appellate court said that it can’t decide the case until the CA Supreme Court decides if the bad guys even have standing to appeal. TakePart does a good job explaining it:
In August, Judge Vaughn Walker of the U.S. District Court in San Francisco ruled that California’s gay marriage ban — Prop 8 — violated the U.S. Constitution. Neither Gov. Arnold Schwarzenegger, who was the named defendant in the case, nor Attorney General Jerry Brown, decided to appeal the decision. The only people who were unhappy with the judge’s ruling were the private groups who supported Prop 8 during the election. So they asked the appellate court in San Francisco to take up the case.
Except, anyone who brings an appeal needs to demonstrate what’s called “standing” or the legal right to initiate a lawsuit based on that party’s interest in the case. Since the proponents of Prop 8 weren’t actually the defendants in the case (since they are private parties, and not the government officials charged with enforcing the gay marriage ban), the federal appeals panel said it was unclear under state law whether they had standing to bring the appeal.
So the federal appeals judges want the California Supreme Court to answer that question before the case can proceed.