How can congress pass laws over a presidents veto?
They need a 2/3's majority to override his veto.
Actually, presidents do not make the laws. Only congress can make the laws. Presidents will promote or push their priorities and try to encourage congress to turn those priorities into laws. Presidents need to work closely with congress, since no bills will pass unless congress agrees to pass them, no matter how much a president might want something done.
Presidents do not pass laws. The job of passing laws is up to congress. On the other hand, presidents have an agenda when they are elected, and they try to persuade congress to move that agenda forward. President Obama has had mixed success with getting congress to do what he hoped: he was able to get congress to pass Health Care Reform, for example, but other elements of his agenda have stalled amidst congressional bickering.
Presidents cannot pass legislation. It is congress that makes the laws, and then the president either signs them or vetoes them. But presidents can and do encourage congress to pass certain bills; President Obama, like all presidents before him, has had a number of pieces of legislation he wanted congress to pass. In some cases, they did; in others, they did not.