Recommended: Book of R
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No affiliation btw.
These might be useful. First has a bunch of examples for how to do different things. You can just copy what they do and play around with different params. Second has a bunch of technical docs to read more deeply about different things. It has a huge introductory manual to the R language as well as manpages for all the standard functions.
http://www.cookbook-r.com
https://stat.ethz.ch/R-manual/R-devel/doc/html/index.html
Tip: When searching for help, use "r-project" because "r" is obviously a little less than useful.
Books. I haven't used these, but I've seen them recommended:
https://www.amazon.com/Book-First-Course-Programming-Statistics/dp/1593276516/
https://www.amazon.com/Data-Science-Transform-Visualize-Model/dp/1491910399