How do you specify Object Oriented Programming languages class and structure ?

I am graduated from the USA university of Binod Engineering technology and finding a way to specify classes using Object-oriented programming languages Class and struct element. How could I learn the operator expression at home during the lockdown without the internet?

You could download a good learning site, such as https://www.learncpp.com (where you find classes and struct and whatever) with https://www.httrack.com/page/2/ and you learn at your home :)