I suppose you don't read manga and that's why you don't know.
The Ten-Tails (十尾, Jūbi) is the primordial entity tied to the legend of the Sage of the Six Paths. Its chakra was divided into the nine tailed beasts and its body sealed into what would become known as the moon, by the Sage in his final moments of life. The Ten-Tails is considered to be the creator of the world, and the herald to its end should it ever be revived. Obito Uchiha's ultimate ambition, which was created and designed by Madara Uchiha, the Eye of the Moon Plan, is to capture and merge all nine of the tailed beasts' chakra back into the Ten-Tails' body, and become its jinchūriki and then cast the reflection of his Sharingan on the moon, casting a genjutsu known as the Infinite Tsukuyomi which will put the entire world under his control.
Centuries before the founding of the hidden villages, the Sage of the Six Paths saved the world from the Ten-Tails. He managed to subdue the beast and seal it within his own body, becoming the first jinchūriki. However, this offered merely a temporary solution to the menace: in the event of his death, the seal would dissolve and the Ten-Tails would once again be unleashed upon the world. Knowing this, the Sage searched for a more permanent solution. Ultimately, the Sage succeeded by using his Creation of All Things ability to separate the Ten-Tails' chakra from its body and divide it into nine separate constructs that would later become known as "tailed beasts", scattering them throughout the world. As a final precaution, using Chibaku Tensei, the Sage entombed the physical remains of the Ten-Tails within a colossal stone prison and hurled it into the heavens, creating the moon. The astonishing feat of not only successfully sealing the Ten-Tails, but also suppressing it, made the Sage a deified hero throughout the shinobi world.
Centuries later, the Rinnegan would once again manifest itself in one of the sage's descendants: Madara Uchiha. With his new power, Madara summoned the empty vessel of the Ten-Tails back into the world and named it the Demonic Statue of the Outer Path. Joined by Obito Uchiha, who continued his work after his natural death, Madara devised a means to reunite the Demonic Statue and the tailed beasts back into their one original form so he can use the Ten-Tails to enact his life-long objective: the Eye of the Moon Plan.
(sources: Narutopedia) I didn't want to tell about its abilities, because you haven't still read mange yet, so you may not be able to understand. If you still want to know everything, check out this
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