Short answers, pulled from the story.
The Act of Mediation was a decree issued by Napoleon Bonaparte on the 19th of February 1803 that abolished the Helvetic Republic and replaced it with the Swiss Confederation. Napoleon framed his role as that of a mediator rather than a conqueror, and the document established the political framework Switzerland operated under until 1813.
Napoleon issued the Act of Mediation after the Helvetic Republic collapsed in a civil conflict known as the Stecklikrieg following the withdrawal of French troops in July 1802. He aimed to stop Swiss instability from threatening his emerging empire and to create a pro-French buffer state on the border with Austria and the German states.
The Stecklikrieg was a civil uprising named after the Stäckli, or wooden club, carried by rural insurgents who revolted against the Helvetic Republic after French troops departed Switzerland in 1802. Clashes occurred at the Renggpass near Pilatus on the 28th of August, in artillery attacks on Bern and Zürich in September, and at Faoug on the 3rd of October, forcing the central government to retreat from Bern to Lausanne on the 18th of September before collapsing entirely.
The Act of Mediation recognized 19 cantons in total. It restored the original 13 members of the old Confederation and added 6 new cantons: St Gallen, Graubünden, Aargau, Thurgau, Ticino, and Vaud.
The Tagsatzung, or Diet, was the highest federal body established by the Act of Mediation. It rotated annually among six leading cities called vororten: Fribourg, Bern, Solothurn, Basel, Zürich, and Lucerne. The chief magistrate of the host city served as Landammann der Schweiz and presided over the Diet.
The Act of Mediation effectively ended when Austrian forces crossed the Swiss border on the 21st of December 1813 as Napoleon's power waned. On the 29th of December 1813, the Diet abolished the 1803 constitution under Austrian pressure. A replacement was eventually shaped through the Congress of Vienna, and Switzerland entered the period known as the Restoration of 1815.