Almost everything in R is done through functions. Quick-R gives a very useful overview of commonly used numeric and character functions for creating or recoding variables.
And while you are at it, check out the rest of the website. It provides information about, and helps new users to quickly learn more about the R Interface, data input, data management, basic and advanced statistics and basic and advanced graphs in R. It aims at ‘experienced users of popular statistical packages such as SAS, SPSS, Stata, and Systat’, but it is also very useful for current R users.
Edit: I just came across this site, which offers a guide for novice and intermediate users of R in the form of a mind map. The mind map is arranged in eight sections, or main branches, arranged by task. Each branch covers a general set tasks, such as learning to use R, running R, working with data, statistical analysis or plotting data. It looks like a very handy information tool. It is quite heavy on your computer resources, but the author already mentioned he might split the mind map up to reduce memory consumption.