The US Army’s 75th Ranger Regiment and the US Army Special Forces both are part of the US Army Special Operations Command. Their organizations are different, reflecting the different types of missions they are expected to execute.
Rangers in the US Army consist of the 75th Ranger Regiment’s Special Troops Battalion and First, Second and Third battalions, and the US Army Ranger School’s Fourth, Fifth and Sixth battalions of personnel undergoing individual Ranger training.
The 75th Ranger Regiment is organized and trained to conduct missions in unit sizes from squads to the entire regiment, as an elite light infantry fighting unit. Their missions include airborne and air assault operations, seizing key terrain such as airfields, destroying strategic facilities, and direct combat against enemy forces.
Individual personnel train in specialized Ranger Assessment and Selection Programs leading to the US Army Ranger School course, successful completion of which will earn full Ranger qualification and the right to wear the Ranger tab on the uniform, whether or not they are serving in a Ranger unit.
The Army Special Forces
The Army Special Forces are set up to provide training in a broad range of military skills and leadership to non-US forces, although Special Forces personnel have often fought side-by-side with the troops with whom they are working. The Special Forces have five primary missions:
Foreign Internal Defense
(The Airborne tab, shown here with the US Army Special Forces shoulder patch, is used to identify US Army units that are designated as “airborne units.” This is not an individual qualification tab; Graduates of airborne training are awarded parachutist’s wings.)
Individual soldiers who complete the Special Forces qualification courses may wear the Special Forces tab for the remainder of their military careers, whether assigned to a Special Forces unit or not.
– Source: Quora