Let x,y be a point on parabola. now according to defination of parabola
distance from focus = perpendicular distance from a fixed line(directrix)
( (x-0)² + (y-0)² )¹/² = x-6
(x-0)² + (y-0) = (x-6)²    (on squaring both side)
x² ₊ y² = x² +36 -12x
y² +12x -36 =0 eqation of parabola 
in very first step on left side i have used distiance formula and on right side find a distance of point from given eqation