Like a miniature version of the tar pits of La Brea, resin traps various creatures and objects in it before becoming amber. This piece of amber contains a fairly complete fossil insect. Despite what you saw in the movie "Jurassic Park," extracting DNA from amber fossils is not routinely, or even occasionally successful. So although amber specimens contain some amazing fossils, they are not good examples of pristine preservation.
Insects were the first creatures to take to the air, and their rare fossils date back to the Devonian, about 400 million years ago. The unusually good Wikipedia article on insect evolution suggests that the first winged insects arose with the first forests, which would make their association with amber even more intimate.
Learn more about insects and their history from About.com Insects Guide Debbie Hadley.