Short answers, pulled from the story.
Most plant resins are composed of terpenes including alpha-pinene and beta-pinene. These molecules form the backbone of the substance while smaller amounts contain tricyclic sesquiterpenes like longifolene.
Resins protect plants from insects and pathogens by flowing out when a tree trunk is cut or damaged. The liquid repels herbivores and stops bacteria from entering wounds while volatile phenolic compounds may attract predators of attacking insects.
The oldest known use comes from the late Middle Stone Age in Southern Africa where people used it as an adhesive for hafting stone tools. Human use has been documented since ancient Greece with Theophrastus writing about these substances over two thousand years ago.
Examples include copal from Protium copal and Hymenaea courbaril, dammar gum from Dipterocarpaceae, and mastic from Pistacia lentiscus. Sandarac resin grows on Tetraclinis articulata which is the national tree of Malta while kauri gum comes from Agathis australis in New Zealand.
Many materials are produced via conversion of synthetic resins to solids such as Bisphenol A diglycidyl ether becoming epoxy glue upon addition of a hardener. Alkyd resins harden by exposure to oxygen in the air while silicones prepare from silicone resins via room temperature vulcanization.