Do I need proof to buy sulfur? Can ordinary people buy it? What is the function of sulfur?

No, sulfur is a common chemical with a wide range of uses. For example, in agriculture, forestry, orchards and so on. Sulfur is used to make stone sulfur mixture to control tree diseases and insect pests, and can also be boiled with fine sand to make adhesive. This glue is used for bolts on cement sleepers in railway engineering, and it is also smoked and bleached, so it is widely used in civil use.