Git is a system. It is used both to provide a complete and iterable history of development, and also to enable multiple users to edit the same files simultaneously.
The add command is used to point out what new changes should be recorded in the repository. The arguments are what files should be added, and the dot means "all changes", while the -v flag stands for verbose and will output the name of every file that is successfully added by the command.
git add . -v
The commit command groups all added changes into one package, and the -m flag lets you describe the changes with an informative string.
git commit -m "Add some changes"
The push command is what actually uploads the changes to the repository.
git push origin master