I came from Python using iPython. I missed them for the first few weeks, but now I can't switch from RStudio. It really is just such a great tool for data science.
You use back ticks to make your code chunks.
For example: Some random Markdown text here is treated as a text block in Juypter
```{r}
summary(cars)
```
Then some further text goes here.
Jupyter has some conveniences, but the tradeoffs aren't worth it for me. Working in a web browser has much less power, when it comes to keyboarding, than Atom/Sublime. And I generally don't need to interact with my data; I know what I'm outputting, I just want to show the results to readers alongside my code. I don't use RStudio but RMarkdown is easy to run from the command line.
By contrast, Jupyter requires (AFAIK) working within the browser and, when you save the file, you get a huge jumble of JSON, which is how the notebook is serialized. I tend to write a lot of vignettes/explorations and the need to full-text grep them is important to me and is not feasible when the text content is saved as JSON.
You can convert the Notebooks to different formats. Though they tend to have to be fixed up a bit for a script (Which I also might need to in R to turn it into a script)