What is a version control system? How is Git useful?

Question

like for example i am doing ruby on rails and using git for version control.

Answer 1

Version control systems really shine when you're working with another person, or thousands of people; as people work on files, chances are good they'll work in similar spaces. Source code control systems let you merge changes from multiple developers into one coherent product, roll back mistakes, figure out who wrote which specific lines of code (to ask them why their code doesn't work two months later), provide excellent business continuity, etc.

But they are still wonderful with just one developer: check in comments about why you did something in some particular fashion can be worth their weight in gold six months later. You can checkin large changes that depend upon four separate files all at once, and then, if you need to undo it, one single command will back out the changes on all four files at once.