This page of the guide to Biomutant contains a detailed walkthrough of the main story quest Another World.
The-Old-One immediately recognized that the main character learned Wung-fu from his Muma. He told the story of the old village and how Muma trained all the tribe leaders in various Wung-fu disciplines.
Talk to Out-Of-Date
As you talk to the Out-Of-Date, you will learn that the person you are talking to remembers you well from your childhood. He mentions that he has heard rumors of a one-eyed Ronin being seen beyond the Great Wall and is glad to see that it is true. The Out-Of-Date will tell you about the scar that adorns the character you control, about Moom and Popsi, and about what Lupa-Lupin did in the past - which was the beginning of the end. After the destruction of the Old Village, Mooma's disciples formed tribes and turned against each other over time. If it weren't for the Tree of Life, no one would have survived.
A conversation with The-Old-One will trigger the main character's forgotten childhood memories.
Talk to Best-Before
The Best-Before will tell you about the Nono creatures and how they can be found in the tall Glittergrass. He will ask you to try to catch one of these creatures.
Ruffle the Glittergrass
Go to the location indicated on the map, stand next to the Glittergrass and perform a melee attack.
After a short conversation, you will get Hoop Net from your friend which you will have to use to catch the Nono. Get as close to the creature as possible and press the interaction key, and Nono will land in your net.
Merge the Nono with the Tree
Go to the indicated location and interact with the tree. After a while, you'll watch a short cutscene in which you'll see that the tree grows additional roots. From this point forward, The-Old-One will care for the Tree of Life.
Talk to Out-Of-Date
When you return to reality, The-Old-One will say that he remembers each day dedicated to nurturing the Tree of Life, but now he fears that his work may be destroyed. The Tree of Life started dying shortly after the World Eaters appeared. There is one World Eater at the end of each root of the Tree and they must be eliminated to save the world.