How did Giuseppe Garibaldi contribute to unification in Italy?

From Internet:

Giuseppe Garibaldi, (born July 4, 1807, Nice, French Empire [now in France]—died June 2, 1882, Caprera, Italy), Italian patriot and soldier of the Risorgimento, a republican who, through his conquest of Sicily and Naples with his guerrilla Redshirts, contributed to the achievement of Italian unification under the royal house of Savoy.