how did FDR get all of his policies passed?

In fact, he didn't. Many of his policies were regarded as unconstitutional and stopped by the Supreme Court. In 1937, his administration tried to change the way Supreme Court justices were apportioned to make his policies pass (through the "Judicial Procedures Reform Bill of 1937").

It was killed in the Senate committee. Its failure is currently considered by NIE economists (such as Daron Acemoglu) as one of the finest hours of American institutions. So no, FDR was no super hero who put in practice whatever policies he wanted.

However, his congressional support can be attributed by the extent of his public support. He won his first two elections in landslides (1936 was the greatest electoral landslide in a contested election, followed closely by Reagan-1984) and had major support in both parties (the New Deal Coalition). There was opposition, but the public was generally with him.