How to find distance between two points?

// VectorMath.
   // Vector manipulation functions:

   // Returns a+b.
   VectorAdd(Vector3F a, Vector3F b);

   // Returns a-b.
   VectorSub(Vector3F a, Vector3F b);

   // Returns a scaled by scalar (ie, a*scalar).
   VectorScale(Vector3F a, float scalar);

   // Returns a scaled such that length(a) = 1.
   VectorNormalize(Vector3F a);

   // Calculate the dot product of a and b.
   VectorDot(Vector3F a, Vector3F b);

   // Calculate the cross product of a and b.
   VectorCross(Vector3F a, Vector3F b);

   // Calculate the distance between a and b.
   VectorDist(Vector3F a, Vector3F b);

   // Calculate the length of a vector.
   VectorLen(Vector3F v);

   // Create an orthogonal basis from the given vector. Return a matrix.
   VectorOrthoBasis(AngAxisF aaf);

// Calculate the distance between a and b.
   VectorDist(Vector3F a, Vector3F b);