Open the terminal, enter:

cd ~/Desktop
ftp "http://www.stat.ucla.edu/~davezes/SSsimple_0.5.tar.gz"

Now install.  Enter into terminal:

R64 CMD INSTALL SSsimple_0.5.tar.gz

(If for some reason you don't have the 64bit version of R, replace "R64" in the above command with just "R")

Now, open R and retreive help on "SSsimple".

Also, a tutorial is available by typing into R:

vignette("SSsimple")