git status
git add -A stages all changes
git add . stages new files and modifications, without deletions
git add -u stages modifications and deletions, without new files
git add -A is equivalent to git add .; git add -u
git add -A is equivalent to git add --all
git add -u is equivalent to git add --update
References
https://stackoverflow.com/questions/572549/difference-between-git-add-a-and-git-add
https://git-scm.com/docs/git-stage
https://git-scm.com/docs/git-add