R can do a lot of really amazing things, but to use just about any of R's many features you need to first import your data and get it into the appropriate shape. For R beginners, this "data wrangling" task can be daunting. Fortunately, ComputerWorld's Sharon Machlis has created an in-depth tutorial for many data preparation tasks, which is well worth working through to get a sense of data-handling in R.
This 8-page tutorial provides step-by-step instructions in the R language for adding columns to a data set, aggregating data by subgroup, sorting data, and reshaping data (converting "wide" data sets to "long" data sets, and vice versa). Unlike older R tutorials, this guide uses newer contributed R packages (including Hadley Wickham's reshape2 package) for many tasks. That's a good choice: especially the at the earlier stages of learning R, it's well worth learning these modern data manipulation tools rather than the more complicated standard R syntax. Check out the full tutorial at the link below.
ComputerWorld: 4 data wrangling tasks in R for advanced beginners