Short answers, pulled from the story.
The Tribunat was one of four assemblies created by the Constitution of Year VIII in France, established officially on the 1st of January 1800. Its function was to send three orators to discuss proposed laws in the presence of the Corps législatif, though it could not vote on legislation. Final authority always rested with the First Consul.
Pierre Daunou, a historian, served as the Tribunat's first president. His independent spirit led Napoleon Bonaparte to dismiss him from the post in 1802.
Napoleon purged the Tribunat in 1802 because of its opposition to the projected Code civil. He used a procedural maneuver: the Tribunat was partially renewed at regular intervals, but it was not publicly known which members would be removed first, so Napoleon was able to select his opponents for dismissal.
On the 7th of January, Benjamin Constant delivered a speech in the Tribunat denouncing "the regime of servitude and silence" that Bonaparte was preparing. The speech made him the leader of the opposition within the assembly.
The Tribunat was suppressed by a Senate decree in 1807, after its eighth session, which ran from August to September of that year. Its remaining functions and members were absorbed into the Corps législatif.
Members of the Tribunat were not chosen by direct universal suffrage. Citizens voted for communal notables drawn from one tenth of their number, who then chose departmental notables from one tenth of their number, who in turn chose national notables from one tenth of their number. The Senate then selected Tribunat members from these national lists.