(Make sure you have installed Xcode from the Mac App Store, and
installed the command line tools from within Xcode.)
Close R
Download the tar.gz onto the Desktop
Open the Terminal application
Enter "R CMD INSTALL Desktop/[pkg.tar.gz]" without the quotation
marks, where [pkg.tar.gz] is the full filename of the tar.gz (such
as "blockTools_0.5-7.tar.gz")
Open R
Enter at the R prompt
> library(blockTools)
Then, you can check that you have installed the desired version using
> sessionInfo()