Ragnarok all began when one day Loki killed Baldr. This set all the other gods into an uproar.
After that there were three consecutive winters that reeked havoc among the people. Families were fighting and killing each other just to have somethng to eat.
Once the humans were mainly gone and the few that remained alive were complete savages, the wolves Hati and Skoll came out. They ate the sun and the moon which made the world dark.
Loki's actions caused him to be locked away in a cave to keep him away from everyone else. After the third and final event, which were earthquakes more powerful than any before, Loki was freed along with Fenrir. As soon as he was free, three roosters would crow which called forth all of the warriors Loki had such as the giants.
After a very long and dangerous battle filled with fire and chaos many gods had died along with the evil forces Loki called upon. The only ones to survive were Vidar, Vali, Magni, Modi, Hodr, and Baldr who had especed Hel. Ragnarok brought the end of the world.