RStudio has curated cheatsheets for common R packages, providing a single page of some of the most commonly-used commands. Among others, you can find cheatsheets for data visualization with ggplot2, data transformation with dplyr, data import with readr, and R Markdown.
All R packages should have published documentation. In addition to documentation available directly within R (at the console, type ?packagename), the developer may provide documentation for a given package. You can also search the RDocumentation site.
Most of the packages described on this site are part of the Tidyverse; you can find documentation and examples within the Tidyverse documentation, including pages for:
There are a number of texts that provide an introduction to R, coding, and data analysis. Some local favorites include: