White Willow Bark

What does white willow bark do? I've seen in it in dietary supplements.

The bark of White Willow (Salix alba) contains salicylic acid, from which aspirin, acetylsalicylic acid, was synthesized. Like other salicylate containing herbs, its actions are pain relief and anti-inflammatory. It is used in arthritic diseases, nerve pain, headache and sore muscles and joints. Willow is also used to reduce fever.