What were the revelations that John Dean gave to the Ervin Committee?

Essentially, John Dean testified that Richard Nixon, contrary to his assurances, was directly involved in the cover-up of the Watergate burglaries. He detailed how the Nixon administration (which included Dean himself, Nixon's chief counsel) evaded, stonewalled, and prevaricated around telling the truth about Watergate. He implicated Nixon and his Attorney General John Mitchell in particular, alleging that they had Most of what Dean testified--he was very specific about the amount of hush money paid to various players in the scandal--had been revealed to investigators already, but his testimony before the committee was a major turning point in the scandal. He was the most highly-placed figure in the administration to go public with what he knew. Later, his charges would be corroborated by audio tapes recorded by Nixon himself. Dean wound up serving a short prison sentence for his role (he openly confessed it) in the cover-up.