Short answers, pulled from the story.
Resin is a solid or highly viscous liquid composed primarily of terpenes, including alpha-pinene, beta-pinene, 3-carene, sabinene, limonene, and terpinolene, along with sesquiterpenes such as longifolene, caryophyllene, and cadinene. Some resins also contain a high proportion of resin acids, which are oxidized terpenes.
Plants secrete resin in response to injury, using it as a defense against herbivores, insects, and pathogens. The volatile phenolic compounds in resin can also attract predators of the insects attacking the plant, serving as a chemical signal for reinforcements.
Natural plant resins include amber (fossil resin from coniferous trees), frankincense from Boswellia sacra, myrrh from Commiphora shrubs, mastic from Pistacia lentiscus, sandarac from Tetraclinis articulata (the national tree of Malta), dragon's blood from Dracaena species, and kauri gum from Agathis australis trees.
Rosin is a solidified resin from which the volatile terpenes have been removed by distillation. It is a transparent or translucent mass with a faint yellow or brown colour, insoluble in water but soluble in alcohol and essential oils. Standard plant resin retains its volatile terpene fraction.
Subfossil copal becomes tacky when a drop of acetone or chloroform is placed on it, whereas genuine fossil amber does not react this way. Both amber and copal are forms of fossil or subfossil resin, but amber is fully fossilized while copal is only partially so.
The oldest known use of plant resin is as an adhesive for hafting stone tools, documented from the late Middle Stone Age in Southern Africa. The same material that served this prehistoric purpose was also prized in ancient Egypt as frankincense and myrrh, required for certain religious rites.