The amorphous, three-week-old occupation of a New York park just blocks from Wall Street is growing. The occupation is also spreading to other cities — Boston, Chicago, Los Angeles, and smaller places like McAllen, Texas. The arrest on Saturday of more than 700 Occupy Wall Street (OWS) protesters on the Brooklyn Bridge pushed the movement into the international spotlight, but the lack of a spokesperson, leader, or easily digestible message has confounded the news media. As Slate's David Weigel puts it: "The arrests were the hook. What's the story?" Here's what you should know:

What is Occupy Wall Street's driving issue?
Unhappiness with Wall Street's power and greed, certainly, as well as the eroding of the middle class. But other than that, the conventional wisdom is right, says Slate's Weigel. "There is no agenda uniting the people showing up and expressing their anger at finance." They have a "mostly official" blog, a "Declaration of the Occupation of New York City," an open "We are the 99" tumblr forum, and even a FAQ of sorts, says Ezra Klein in The Washington Post. But it's primarily "a protest movement without clear demands, an identifiable leadership, or an evident organizational structure."

So what do they want?
"No one knows," says Slate's Weigel. The movement is "happily incoherent," packed with disparate members including Ron Paul 2012 supporters, young anarchists, and veteran lefty activists. "That old standby, 'People Before Profits,' seems to capture the gist fairly well," says Nathan Schneider in The Nation. But the growing consensus among the protesters is that "government institutions are already so shot through with corporate money that making specific demands would be pointless until the movement grew stronger politically."

Is it a Tea Party for the Left?
Not exactly, or at least not yet. Broadly speaking, OWS is actually "driven by the same fuel that gave fire to the Tea Party," says Michael Scherer at TIME: "Anger at elites, a feeling of injustice, a concern about jobs, fear about the direction of the economy, and a clear desire to take action." OWS is furious at corporate America, though, while the Tea Party vents its rage at government. But to gain Tea Party-like influence, OWS will probably need a coherent message and some level of professional organizing.

Is anyone calling the shots?
The original call for occupying Wall Street was from a group called Adbusters, and other groups have aided, such as "hacktivist" collective Anonymous, says Schneider in The Nation. But the organizers have vested most of their power with the NYC General Assembly, which is a "horizontal," leaderless body that makes decision through consensus.

What's next for Occupy Wall Street?
"No one knows what will happen next," says TIME's Scherer, but the movement is spreading to other cities, and it has plenty of room to grow. And on Wednesday, liberal group and several labor unions are marching to join the protesters near Wall Street. And after that... well, it's anyone's guess.

Sources: CNNThe NationNew York TimesOccupy Wall StreetSlate (2), TIMEWashington Post (2,3), We Are the 99 Percent