Short answers, pulled from the story.
The uprising began when French general Joachim Murat attempted to move King Charles IV's daughter and her children along with his youngest son to Bayonne, France. Citizens viewed this action as an insult to their royal family and gathered before the Royal Palace on the 2nd of May 1808 to stop the removal of Francisco de Paula.
Pedro Velarde y Santiyán was a 28-year-old artillery captain who joined the fighting after hearing gunfire while Luis Daoíz y Torres served alongside him during the defense of the Monteleón artillery barracks. Both officers died during the French assault on the barracks and their unit became one of the few Spanish troops to disobey orders against vastly superior numbers.
Marshal Murat created a military commission on the evening of the 2nd of May 1808 which issued death sentences for anyone captured bearing weapons. General Grouchy presided over this body and hundreds of prisoners including craftsmen found with shearing scissors or kitchen knives faced summary execution the following day.
Francisco de Goya painted The Charge of the Mamelukes to portray street fighting in Puerta del Sol and his work The Third of May 1808 captured the scene of hundreds being executed. These images documented the violence of the uprising for future generations and remain a primary historical record of the events.
Juan Pérez Villamil encouraged mayors Andrés Torrejón and Simón Hernández to sign a declaration of war called Bando de los alcaldes de Móstoles or Edict of Independence in Móstoles. This rebellion gave considerable impetus to resistance across Spain and Portugal while British intervention followed with the Battle of Roliça led by Wellington.