How did the Reagan Administration violate Congressional instructions and stated administration policy in its decision to fund the Contras?
During the 1980s, there was a major controversy in the US over the Nicaraguan "Contras" who were fighting the Sandinista government. The Reagan Administration and Republicans saw the Sandinistas as dangerous communists near to the US. The Democrats thought this was the same mistake as had been made in Vietnam and argued that the Sandinistas were more nationalist than communist. The Congress (controlled by Democrats) passed the Boland Amendment prohibiting any part of the Executive Branch that was involved with intelligence from giving aid to the Contras. They did this because they only wanted the Contras to get humanitarian, and not military, aid.
In terms of "stated administration policy," the administration's policy was never to bargain with terrorists.
In the Iran-Contra affair, the Reagan Administration violated both policies. It secretly sold arms to Iran (which it saw as a terrorist nation). It did so in part to try to get the release of some hostages held by Iranian allies in Lebanon. It used some of the money (again secretly) to give aid to the Contras. By doing so, it violated both its own policy by selling to Iran in exchange for help with terrorists and Congress's policy by having a part of the executive branch involved with intelligence (National Security Agency) give aid to the Contras.