Git add not adding files

when I try to git add my files, I typed

git add <insert file names here>

That works correctly. However, when I try to do

git commit -a

My git repository tells me that it's empty. What is outputted is:

# On branch master
# Untracked files:
#   (use "git add <file>..." to include in what will be committed) 
#
<insert name of files here>

nothing added to commit but untracked files present (use "git add" to track)

Might anyone know the solution to this? Thanks.