I am not sure how to use this function. I need to predict concentration as a
function of time

I was given a equation of C(z,t) = Co ERFC(z/s(square root of Dt)

where C = concentration
z = depth
t = time
Co = initial concentration
D = depth (in soil)

THe example given in the help section does not explain how to use it

Could someone please just explain to me how to enter the equation

thanks