How to indent multiple lines of code in Rstudio?

Highlighting the code of interest and hitting tab should add another level of indentation. Shift-tab will remove a level of indentation.

You could use a shortcut. First, highlight the lines you want to indent, and then press: Ctrl + } (at least, that is the combination on my keyboard).

If you want to move in the other direction, then press: Ctrl + {.