Point slope form is just a point and the slope written in the form y-y1 =m (x-x1).
Where x1 and y1 (should be subscripts) are (x1,y1) the point you are given.
So in this case all you must do is plug in the given values:
( y-y1 ) = m ( x-x1 )
( y-4. ) = -1 ( x-2 )
This being your answer
I hope this helps!!