Why did the british troops march on lexington and concord? how do the events mark the start of the american revolution? ? answer both questions pls

The British troops marched to lexington and concord to get battle supplies and that is where the first event of the war happened. A famous gun shot was shot out, but nobody knows who did it. The events mark the start of the revolution becuase it was the first battle of the revolution. 

Hope this helps!