$ mkdir test
 $ cd test
 $ git init
Initialized empty Git repository in /home/pgniewek/test/.git/
 $
 $ echo "1" > 1.txt
 $ git add 1.txt
 $ git commit -m "one"
[master (root-commit) ab603a5] one
 1 file changed, 1 insertion(+)
 create mode 100644 1.txt
 $
 $ echo "2" > 2.txt
 $ echo "3" > 3.txt
 $
 $ ls
1.txt  2.txt  3.txt
 $
 $ cat *
1
2
3
 $
 $ git add 2.txt
 $ git status
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    new file:   2.txt

Untracked files:
  (use "git add <file>..." to include in what will be committed)

    3.txt

 $ git reset
 $ git status
On branch master
Untracked files:
  (use "git add <file>..." to include in what will be committed)

    2.txt
    3.txt

nothing added to commit but untracked files present (use "git add" to track)
 $ cat *
1
2
3