git add method to add undo the wrong file

git add to add extra files 
such errors is because sometimes possible

git add. (space + dot) represents all files in the current directory, not careful it will submit additional documents

git add If you add the wrong file, then

Undo

git status look at the add files 
git reset HEAD if not now, then later what is on the inside of all time add withdrew 
git reset HEAD XXX.html a file is to be withdrawn