In what ways did Italy contribute to WW2 ? How did they help the axis powers?
What was their biggest accomplishment in ww2?

Italy joined the war as one of the Axis Powers in 1940, as the French Third Republic surrendered, with a plan to concentrate Italian forces on a major offensive against the British Empire in Africa and the Middle East, known as the "parallel war", while expecting the collapse of British forces in the European theatre.
Italy joined the Anti-Comintern Pact on November 6, 1937. On May 22, 1939, Germany and Italy signed the so-called Pact of Steel, formalizing the Axis alliance with military provisions. Finally, on September 27, 1940, Germany, Italy, and Japan signed the Tripartite Pact, which became known as the Axis alliance.
Changing sides and joining the Allies as a co-belligerent in 1943 was probably Italy's biggest success in World War II.