Answer 1

Sololearn provides basic knowledge and definitions of every language available on it. I'd rather you go through the first chapter of every language you just mentioned and find thier definitions. That's the difference.

Answer 2

Are you 6th standard? Is it true? Its great.. it it appreciable your curiosity..
wait for my answer..

C is a programing language, named based on B language as you know.

C++ is invented adding to object oriented features to in according to C.

later C# came, is almost mixing of C, C++. combining both features.

CSS is different to all these, is
CSS- Cascading Style Sheets used to add styling to your html pages...