The easiest way of doing this is through the git config command. You need to provide your name and email address because Git embeds this information into each commit you do.

git config --global user.name "Your Name"
git config --global user.email "youremail@domain.com"

You can see all of the configuration items that have been set by typing:

git config --list

returns:

user.name=Your Name
user.email=youremail@domain.com

As you can see, this has a slightly different format.

The information is stored in your Git configuration file, which you can optionally edit by hand with a text editor:

vi ~/.gitconfig

~/.gitconfig

[user]
    name = Your Name
    email = youremail@domain.com

There are many other options that you can set, but these are the two essential ones needed to prevent warnings in the future.