A good place to begin is with the ComputerWorld introduction to R. 

The first page is especially nice for explaining why it is good to use R rather than some other method (such as Excel) for doing statistics.

R for Data Science is the online version of the O’Reilly book, a good text. It uses Rstudio (as we do) and begins with data visualization, which is a good place to enter programming in R. This book contains much more than we need for this course, but it is good to use as a reference.

Datacamp online courses – you can use for free until the end of August, learn whatever you like!