R is Available for macOS, Windows, and Linux.
R: https://mirror.las.iastate.edu/CRAN/
RStudio: https://rstudio.com/products/rstudio/download/
RTools: https://cran.r-project.org/bin/windows/Rtools/ (RTools available for Windows only)
RStudio on macOS requires the Command Line Developer Tools from Apple. You may be prompted to download them when you install or run RStudio.
The department of Mathematics and Statistics has an "R/RStudio Help" page. RStudio also provides interactive RStudio tutorials that cover the basics of data science, cheatsheets for working with popular R packages and a guide to using RStudio Cloud.