acf() returns a list with a element called acf, which contains the value to be plotted...

> a <- rnorm(10)
> acf(a)$acf
, , 1

          [,1]
[1,]  1.00000
[2,] -0.29664
[3,] -0.25788
[4,]  0.07783
[5,]  0.17804
[6,]  0.04112
[7,] -0.30941
[8,]  0.09635
[9,]  0.07759
[10,] -0.10700

test stat for H(afc=0) of an iid sequence is asy~N(0,1/T)

good that you swift to R, which will eventually force you to know the stuff