If highway means 1, then what is the difference between normal national road and highway?
That's the point, they can be used interchangeably.
What is the difference between freeway(free of charge?) and expressway?
highway
2) a limited access road, which is basically built for long-distance traffic, also to avoid towns (in this sense you could also use freeway and expressway with little, if any, difference. In British English you'd use 'motorway')
If you're still not satisfied with the answer you can have a look here, it's an excerpt from
wikipedia:
In the United States, the term
freeway is used nationwide. In some regions of the U.S.,
other terms are also used, including expressway, Interstate Highway, thruway, highway, and turnpike. While some people use these terms interchangeably,
turnpikes and thruways usually have associations with toll roads, such as the New Jersey Turnpike, Ohio Turnpike, Pennsylvania Turnpike, West Virginia Turnpike, Florida's Turnpike, and the New York State Thruway.
Consequently, the term
freeway is often used to refer to a toll-free highway[4][5]
as opposed to its original meaning[6][7] – in which the component "free" implies freedom from traffic interference rather than "at no cost" – still used in other countries and in parts of the U.S.
In the United States, an
expressway is defined by the federal government’s Manual on Uniform Traffic Control Devices as a divided highway with partial control of access.[19]
In contrast, a freeway is defined as a divided highway with full control of access. More
here, scroll down to the bottom of the page.
The vast majority of
expressways are built by state governments, or by private companies,
which then operate them as toll roads pursuant to a license from the state government.
Hope that helps.