having problems with this typedef statement

Hello , Please what does the second typedef statement do,

struct listnode{
char data;
struct listnode *nextPtr;
};

typedef struct listnode Listnode;
typedef ListNode *ListNodePtr;

what is the difference between

ListNodePtr *sPtr;
ListNodePtr startPtr;

Please explain what the second Line of Code would do please
startPtr = NULL;
ListNodePtr *sPtr = &startPtr

You're obviously on a course... courses have text books... go look it up.