You can install rnhanesdata from Github using the devtools package by running the following code:
#install.package("devtools")
devtools::install_github("andrew-leroux/rnhanesdata")
Once this package is installed, see the help file associated with the package (?rnhanesdata) for an overview of the primary package functions, as well as a high level description of the processed NHANES data included in the package. Each set of processed data includes it's own set of documentation.