The main reason I know of for a federal judge to step in when it comes to state laws is when those laws are unconstitutional. For instance, if a state passed a law, or even an amendment to its state constitution which permitted slavery, the federal judge could overturn it as a violation of the 13th amendment.
Federal judges have this power, because of Article VI of the US Consitution wihch reads (in part):
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any state to the Contrary notwithstanding.
In Article III, it specifies that
The judicial Power of the United States, shall be vested in one supreme Court, and in such inferior Courts as the Congress may from time to time ordain and establish.
Taken together, this means that when a state passes an unconstitutional law, it is itself breaking the law (Article VI), and can be taken before a federal court (Article III) to be forced to change its course (you can't exactly arrest a state, after all). And the US Supreme Court (SCOTUS) determines what is unconstitutional.
So much for the general case. In this example, which I am assuming is related to Wisconsin's gay marriage ban being overturned, SCOTUS has found that laws restricting gay marriage are a violation of the Fifth Amendment's "Due Process" clause, which says (in part):
nor shall any person ... be deprived of life, liberty, or property, without due process of law
In Windsor v. United States they held that laws defining marriage as between one man and one woman violate a homosexual's rights to equal liberty (specifically, to marry who they choose). Since these laws are now unconstitutional, and the US Constitution is the supreme law of the land, all state-level laws (and constitutional amendments) are now illegal, and thus they legally must be overturned.
As for addressing it, in Hollingsworth v. Perry SCOTUS decided that you don't have standing to sue the government for its decisions simply because you voted for or championed a given cause. The details are on that wikipedia page, but it boils down to this (my interpretation): "If you can't show how you, personally, were or will be harmed by the law, you can't sue to stop it.
Basically, unless the ability of other people to marry has some detrimental affect on your legal rights, you have no standing to sue.
However, as @cpast pointed out in the comments, the state itself does have standing to appeal (assuming it wants to, which California didn't in Hollingsworth v. Perry), because it is directly affected by this ruling, so you can encourage your governor to pursue it on your (and the state's) behalf.