git status will show you the status of the branch you currently have checked out. Before you switch branches, merge, pull or push you want to make sure you have a clean working directory and you can check with git status.
git add . is a useful command that will version control any new files and remove from version control any files that you've deleted. If you have a file that has been added to git that you have deleted from your repository, it won't be deleted from git until you use git add ..