What does "Changes not staged for commit" mean

when you change a file which is already in the repository, you have to git add it again if you want it to be staged.

This allows you to commit only a subset of the changes you made since the last commit. For example, let's say you have file a, file b and file c. You modify file a and file b but the changes are very different in nature and you don't want all of them to be in one single commit. You issue

git add a
git commit a -m "bugfix, in a"
git add b
git commit b -m "new feature, in b"

As a side note, if you want to commit everything you can just type

git commit -a

Hope it helps.

You have to use git add to stage them, or they won't commit. Take it that it informs git which are the changes you want to commit.

git add -u :/ adds all modified file changes to the stage git add * :/ adds modified and any new files (that's not gitignore'ed) to the stage