To start with you will obviously need to install R (at CRAN) and preferably a GUI like RStudio. For installation instructions for each package see the package README or the package’s documentation web site.
Currently almost all the packages I have developed are available through the CRAN public repositories. However, a few of the packages are still only available from their Git repositories at Bitbucket. The package not yet in CRAN is ‘photobiologyReflectors’. It is also possible to install the current development versions of all packages from Bitbucket either by using package ‘devtools’ or by cloning one of the Git repositories and building the packages locally.