pca in R

Hi,
I am learning how to do principal component analysis in R. However, since I
am family with only a few built-in functions like prcomp, sd, cor, I started
manually with examples in text books while trying to use the few functions I
know to manipulate what they have in the text. From the example in the text
I obtained a data set. Using cor and cov, I calculated the correlation and
covariance of the data frame. I equally calculated standardized data as they
did. They plotted a graph of the standardized X against Y, X against Z and Z
against Y. I tried to plot the same graph in R but could not fit the First
Principal Component as they did.
I will be glad if anybody would be good enough as to guide me on how to fit
this first (and probably second, third) principal component (s). As a
begginer, I would appreciate any additional information on how to proceed
with pca in R.
Thank you.
Ogbos

? ? ? ?[[alternative HTML version deleted]]