R General References

You can start from here:

• R reference card 
• Quick Graphics and Graphics and Murrel's Graphics
• Quick R  
• R-Spatial  and Spatial R
• California Soil Resources Lab
• Manuals 
• Videos and video tutorials and the Google R Videos
• Packages
• Search engines 
• R Site search
• The Guerilla guide to R
• R Inferno give a stimulating alternative vision of R.
• Here you can download the Matlofs book, The Art of R Programming.
• And here you can download a book on ggplot2 by its own author Hadley Wickham, and other ggplot resources.
• Three-Toed Sloth's book is a fresh-air statistical book which uses R.
• Here you will find the book on "Modeling data with functional programming in R" by Bryan Lee Yung Row 
• A curated list of awesome packages and R-related stuff
• A guide to R graphics by Joachim Schork
• Last, but not least, Hadley Wickham book' and Advanced R.

Interesting posts (mainly from R Blogger)

• Basic Histograms
• Installing Packages
• Using apply, sapply, lapply

An finally this nice guide entitled: hipsteR re-educating people who learned R before it was cool.

If you have further questions, ask Stackoverflow

If you managed to learn how to write function, please decide to make a package. Emanuele Cordano found this nice post on github explaining why to do (thinking to  statistics).

An alternative pathway of instructions is here.