How does llvm's SDUse works?

I'm reading llc's code about SDUse,I cannot understand SDUse::addToList(SDUse **List). How does its **pre and *next works to insert a node in a list?

 /// Represents a use of a SDNode. This class holds an SDValue,
 /// which records the SDNode being used and the result number, a
 /// pointer to the SDNode using the value, and Next and Prev pointers,
 /// which link together all the uses of an SDNode.
 ///
 class SDUse {
   /// Val - The value being used.
   SDValue Val;
   /// User - The user of this value.
   SDNode *User = nullptr;
   /// Prev, Next - Pointers to the uses list of the SDNode referred by
   /// this operand.
   SDUse **Prev = nullptr;
   SDUse *Next = nullptr;

.....

   void addToList(SDUse **List) {
     Next = *List;
     if (Next) Next->Prev = &Next;
     Prev = List;
     *List = this;
   }
  
   void removeFromList() {
     *Prev = Next;
     if (Next) Next->Prev = Prev;
   }
 };