Amber owes its existence to the defence mechanisms of certain kinds of tree. When the bark is punctured or infected, a sticky resin oozes out to seal the damage and sterilise the area. Some species of trees produce such copious quantities of resin that small creatures, as well as leaves and flowers from the trees themselves, get trapped. Not all resins can form amber - most types are chemically unstable and will decay over time. However, if lumps of a more stable resin are buried in sediment, they can fossilise and will eventually turn into amber. Tree resin that's decades to centuries old, but has not yet properly fossilised into a true amber, is known as copal.
Fossil hunting is enjoyed by amateurs and professionals alike. In fact, palaeontology is one of the few sciences where amateurs have made - and continue to make - important new discoveries.