Short answers, pulled from the story.
Winston Churchill called Italy the soft underbelly of the axis to argue that invading would remove Italy from the Axis alliance and weaken German influence across the Mediterranean Sea. This strategy promised to reduce shipping capacity needed for Middle East and Far East theaters during a crisis of Allied disposal while tying down German forces.
Operation Baytown launched on the 3rd of September 1943 when British Eighth Army crossed the Straits of Messina. Major-general Gerard Bucknall led the 5th Infantry Division landing north of Calabria's toe while Guy Simonds commanded the 1st Canadian Infantry Division at Cape Spartivento.
Main landings began the 9th of September under Operation Avalanche targeting Salerno on the western coast with Lieutenant General Mark W. Clark commanding U.S. Fifth Army comprising VI Corps and X Corps. Vice Admiral Henry K. Hewitt directed naval task force totaling 627 vessels including cruisers and destroyers to support the invasion.
German bombers targeted Admiral Hewitt flagship serving General Clark headquarters calling thirty red alerts period 36 hours response 450 Luftwaffe flying sorties. Eighty-five Allied vessels hit German bombs off Salerno while Fritz X glide bombs dropped Dornier Do 217s disabled USS Savannah narrowly missing Philadelphia morning the 11th of September.
Fascist troops occupying Naples provoked a rebellion starting the 27th of September which led to a swift advance by British X Corps forcing Germans to evacuate. The main invasion used less than half troops landed during Sicily campaign considering resistance from six German divisions before securing the area.