This is till the most basic standard when it comes to web pages. If you want a page to be readable by any browser, use HTML 2.0. A more senisble and newer standard is HTML 3.2. HTML 3.0 was refined because it was not widely accepted. By its very nature, HTML is strutural language ,not a formatting language.
Browsers are programs for displaying HTML-code.
The first popular browser was NCSA Mosaic. It supported only HTML 1.0. Microsoft saw this gigantic success and soon released its own browser, the MS Internet Explorer, for free. Netscape, on the other hand, did not sleep, and they also had a few things Microsoft's program couldn't do. These was for instance the Frame - function, which allows splitting up the browser windows in different sections and the Tables function for Tables.