Lets go below!

When the dragonfly lays her eggs they will either be placed in or on plants or simply abandoned in the water. 

Nymph casing follow adult emergence

These will hatch into nymph's and the process can take days to weeks according to the species.  The nymphs will live under water until they are ready to emerge as adults.  This can vary from one year to several.  This really depends on the species.  They will moult many times (around 12 times) as they gradually mature.

They are amazing predators.  The dragonfly nymph is a carnivor and will eat just about anything it can catch with its extendible jaws including small fish like Sticklebacks! They breathe though gills and if you catch a dragonfly nymph you will be able to tell if it is a Damselfly or a Dragonfly by looking for the gills or trachael gills.  They resemble feather like structures on the tip of the abdomen (tail) in Damsel Flies.  They are absent in Dragonflies because they are inside the nymph. Nymphs are also the prey to other creatures and in particular the Great Diving Beetle larvae which will take a small nymph as a tasty treat!

Dragonfly Nymph