how do extension work and how do you use them

Answer 1

whenever u r trying to remane or name a file u should write .js .html .css .jar .exe after the name itself. specify the extension according to the type of file you want it to be

Answer 2

Microsoft Windows identifies and uses files with the help of file extensions. A file extension is a part of the file name written at the end of the name after a period.

Answer 3

thank-you for helping me out