Chapter 26 Cheat sheets
RStudio produces a number of cheatsheets; the most useful ones for beginners are below.
Basic R code
http://github.com/rstudio/cheatsheets/raw/master/base-r.pdf
RStudio https://github.com/rstudio/cheatsheets/raw/master/rstudio-ide.pdf
RMarkdown
https://github.com/rstudio/cheatsheets/raw/master/rmarkdown-2.0.pdf
https://www.rstudio.com/wp-content/uploads/2015/03/rmarkdown-reference.pdf
Translations of some of these cheat sheets can be found at the bottom of the RStudio page.