What role did truman play in the vietnam war?

This President was no stranger to making super tough decisions- he was the one who inherited the position after Roosevelt died and he ended the war by approving the nuclear bombings of Hiroshima and Nagasaki- a highly controversial event. 

The French had asked previous President Roosevelt to help them recolonise Vietnam but he declined.

The Viet Minh was initially beaten back by the Allied forces until China entered the mix. Supplied with weapons and other equipment, the insurgents became a conventional army that was able to threaten the French control.

However, Truman was still reluctant to send US troops into Vietnam.

This is the timeline of what happened:

May 1, 1950 — After the capture of Hainan Island from Chinese Nationalist forces by the Chinese People's Liberation Army, President Truman approves $10 million in military assistance for anti-communist efforts in Indochina. The Defense Attaché Office was established in Saigon in May 1950, a formal recognition of Viet Nam (vice French IndoChina). This was the beginning of formal U.S. military personnel assignments in Viet Nam. U.S. Naval, Army and Air Force personnel established their respective attaches at this time.September 1950 — Truman sends the Military Assistance Advisory Group (MAAG) Indochina to Vietnam to assist the French. The President claimed they were not sent as combat troops, but to supervise the use of $10 million worth of U.S. military equipmentto support the French in their effort to fight the Viet Minh forces.Following the outbreak of the Korean War, Truman announces "acceleration in the furnishing of military assistance to the forces of France and the Associated States in Indochina...". and sends 123 non-combat troops to help with supplies to fight against the communist Viet Minh.1951 — Truman authorizes $150 million in French support.
Shortly after, he left the office and handed over reins to the next president. As you can see, in the Vietnam locality, he provided mostly financial support and little military support. I hope that answers your question :)