You only have to set this up once per machine.

TL;DR

git config --global user.name 'Jennifer Bryan'
git config --global user.email 'jenny@stat.ubc.ca'
git config --global --list

In words …

From RStudio, go to Tools > Shell and tell git your name and GitHub email by typing (use your own name and email):

These commands return nothing. You can check that git understood what you typed by looking at the output of git config --global --list.

Resources:

Go back to the index for the all the Git stuff.