This gives you a list of all the R packages available:
$ apt-cache search '^r-'
This installs a basic R system:
$ sudo apt install r-recommended
More things here:
For latest versions, see https://cran.r-project.org/ As part of R's policy of doing everything differently and breaking everything, it's not possible to bookmark the actual page, so you'll have to follow the Download R for Linux link.
deb http://cran.ma.imperial.ac.uk/bin/linux/debian jessie-cran3/
add the gpg key
# apt-key adv --keyserver keys.gnupg.net --recv-key 381BA480
update the packages
# apt update
# apt list --upgradable
# apt upgrade