they said that

z=-1 -> w=infinity

z=0 -> w=i

z=1 -> w=0

and that that

z=i -> w=(1+i)/(1+i)

how the got that the last point should go to (1+i)/(1+i)

and after they know which point goes to what point

on what formula they input the point to find the trasformation formala??

how they deal with the point where the need to put infinity

??