Link to Lost girl episodes http://watchseries.lt/serie/lost_girl

In the very basics its a good verses bad situation with the Dark being bad(don't mind feeding off human and killing them. The Light being good and don't really want to kill the humans they feed off of. Also the dark and light are on the verge of war, there is a very temporary peace going on. Also the dark Fae is not allowed on light Fae territory.

(Sorry for the long awaited reply. College has interfered with my free time.)