According to the fact that there is only one straight line perpendicular to the known straight line on the plane, ② is correct;

Of the four angles formed by the intersection of two straight lines, as long as one angle is 90, it can be proved that it is vertical. ③ It is known that three angles are equal, and by using equal vertex angles and complementary adjacent complementary angles, all four angles can be 90, so ③ is correct;

The length of the vertical section between a point outside the straight line and a point on the straight line is the distance from this point to this straight line, so it is wrong.