typedef defines a name for a type:

  int i;  // i is an int variable

  typedef int Fred; // Fred is now another name for int

  Fred j; // j is an int variable


struct creates a data structure

typedef struct defines a name for a data structure:

  typedef struct { double x, y; } Point;  // 2D point type

  Point p, q; // both p and q contain x,y coordinates: p.x, p.y, q.x, q.y


Further example:

A triangle is defined by three points:

  typedef struct { Point a, b, c; } Triangle;

  Triangle t;

t contains 3 points: t.a, t.b, t.c

each point contains x,y coordinates:

  t.a.x, t.a.y, t.b.x, t.b.y, t.c.x, t.c.y