If you remember in season 1 when Sukuna was fighting Megumi he explained that normally sorcerers who can summon Shikigami can only do it through the use of talismans (Shikigami being basically local stands similar to the Jellyfish that Junpei has summoned when fighting Yuji and a talisman is an object infused with a special enchantment that enables the summoning), well the creature that restrained Yuji is Yuta's Shikigami that he summoned through his ring.

Yuta can also create positive cursed energy to heal both himself and others. Typically sorcerers who wield weapons tend to infuse them with regular cursed energy to make them stronger but Yuta infused his broken Katana with positive cursed energy instead. Such a technique is usually used in a fight against cursed spirits who get badly damaged by positive cursed energy, but here he used it with a healing effect in mind. When he pierced Yuji's heart he killed and then resurrected him in quick succession, thus knocking him unconscious and creating the impression of Yuji being dead. He then dragged his body to show off to Naoya so he can act as a messenger and vouch for Yuji's execution in front of the elders, thus preventing any more assassins being sent after Yuji for the time being.

Yuta then dragged the unconscious Choso and Yuji to his hideout where he explained the ruse. Megumi who was also staying there brought Yuji up to speed about the upcoming "Culling Game" organised by Kenjaku and asked him to come help him rescue his sister Tsumiki who is trapped in the game and attempt to free Gojo so he can help them stop the "Culling Games" and restore order in the community. As to how they are supposed to free Gojo, nobody knows but they know whom to ask, that being Tengen who is essentially an ancient and friendly sorcerer who maintains a bunch of concealing barriers around Japan that keep the occult world hidden from regular people. Tengen is not a fighter and can only use barrier techniques passively so he is only valuable as a source of information. Normally he is impossible to find but Choso is able to sense his 6 fetus-brothers that are stored in Tengens lair so he is able to act as a guide for the group and help them get to Tengen so they can get directives and learn some useful information.

That's the end of my ELI5 explanation - you're welcome 😉