# How to interpret ggbiplot() visualization of PCA in R? [duplicate]

To apply and visualize PCA in R often ggbiplot() is used. What is the meaning of this plot ? Why it is useful for PCA ?

We can consider this example: https://tgmstat.wordpress.com/2013/11/28/computing-and-visualizing-pca-in-r/

In particular, what is the meaning of arrows and circle?