Git - is a version control software which is a command line tool. Still complicated? Let's clarify it with examples:
You have an apple in your hand. So it is version 1.0.0
You took a bite
Now it's 1.0.1
You painted same apple in diff color
Now it's a version 1.0.2
That's what's up, just switch apple for a code
This is a main idea of version control, and that what git does for us. It keeps control of all of these version. Because there are other people who might be biting, painting and doing other stuff to that apple. By the way, that apple is a software in real life :)
Github - is a web based code hosting platform(storage). In simple words: you know what storage is? - Same thing, but it's just a storage for code, and it's on cloud :)
See how we use it in the following set of articles.