If you're an absolute beginner to the R language, this Intro to R video series from Google Developers is a great place to get started. Just download R for your system, start the playlist below, and follow along with the on-screen examples. (The video uses the MacOS X version of R, but you should be able to follow along just fine on Windows as well.)
Each video is between 2 and 4 minutes long, and clearly covers a specific topic about R. The series starts in Section 1 with the absolute basics (entering commands, vectors, variables and arithmetic). Sections 2 and 3 progress to slightly more complex object types (data frames and lists) and programming constructs (loops and flow control). By the time you complete Section 4 you'll be able to write and use your own functions in R. I've embedded the complete series below:
Note that the videos also feature closed captioning, which can be helpful to follow along with new function names and technical terms about R.
If you'd like to take a look at the individual videos in the series, you can find the playlist index at the link below.
Google Developers (YouTube): Intro to R (playlist)