This is an R Markdown document. Markdown is a simple formatting syntax for authoring web pages (click the Help toolbar button for more details on using R Markdown).
When you click the Knit HTML button a web page will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:
summary(cars)
You can also embed plots, for example:
plot(cars)