The Great Beast
Head over to Jayma's map marker to begin the quest.
Interact with the broken tree trunk to begin the mission.
Follow the map marker to meet some wenja hunters.
They will instruct you to lure a mammoth to their hunting ground.
Head over to the next map marker to find the mammoth going about its business. Politely ask it to come with you by chucking a spear at it.
Run back to the hunters when it begins chasing you. This can be done safely if you have the beast ride ability and run while riding your beast, or shoot the mammoth from afar so it has to travel a long way to get you. Of course you should be running back to the hunters.
When the mammoth arrives, bring it down with the help of the hunters.
Skin it to complete the mission.