Long story short. It appears that Putin plans to annex 4 regions of Ukraine into Russia very soon. He thens says that he will use nukes to defend if anybody tries to attack or take back those territories because those attacks will be attackes on Russian soil. He says he is not bluffing and I don't think he is.
China won't allow it, its why what is going on there is happening, they want pro Putin Xi out and someone else in.