R comes with a built-in help function. Simply type a question mark followed by the name of the object or function you're having difficulty with, and the documentation about that object or function will appear. For example,
?hist will bring up the histogram documention, which includes information about the usage of histograms, the arguments that can be used to customize histograms, and examples of their use.
While online resources really are better for learning R, there are also some books available: