Its a computer program that shows the current version of text in a file compared to the changes in the past in the same file. How complex do you want to go is

Its a computer program that shows the current version of text in a file compared to the changes in the past in the same file. How complex do you want to go is always the question? What is a screwdriver? Its a tool that turns screws. What's a scew? A piece of metal that connects two thingsgs. OK I got one but its not turning? Oh yeah their are different screw types. .... And on and on for any seemingly simple subject.