George Washington made significant contributions to the American Revolution, with one of his most notable roles being that he was the commander-in-chief of the Continental Army. Among the options you've provided, the most relevant contribution is:
He led American soldiers in Valley Forge.
At Valley Forge, Washington's leadership during the harsh winter of 1777-1778 was crucial for maintaining the morale and resilience of his troops. Although Washington did negotiate agreements with certain Native American groups and made decisions regarding the inclusion of enslaved people in the army, his primary role as a military leader and strategist was pivotal in the overall success of the American Revolution. He was not the leader of the Continental Congress; that role was held by other figures such as John Hancock or later, Henry Laurens.