Basically, when Reagan was president, he allowed the US to trade weapons to Iran in exchange for six US hostages who were being held. This was a problem because Reagan did this in secret and didn't have the authority to do it. After everyone found out what happened, Reagan flip-flopped for a while about whether or not he should claim that he knew what was going on. Then, when investigators tried to figure out exactly what had happened, it was discovered that Reagan's administration had withheld and destroyed evidence regarding the scandal.
