Format HTML called HyperText Markup Language is specially created language for developing and creating webpages. Its viewing can be done via web browsers, for example Internet Explorer. Subsequent editing can be achieved in common notepad. Typical extension is .html.
In 1989 were first tests in communicating over network in CERN, which is research center in Switzerland. There were Tim Berners-Lee and Robert Caillau working on these tests and they used older format SGML for their new job. A year later both of them developed the first version of HTML. They also developed HTTP protocol (HyperText Transfer Protocol), which serves for transferring files of HTML. From 1991 to 1993 were developed first versions of this format, subsequently on it Marc Andreessen a Eric Bina created Mosiac browser. He was targeted on Mac and PCs and was one of the best browsers of these times.
Its main function is showing webpages using HTML language. Best browsers for this format are web browsers. For example, the best known is Internet Explorer which is delivered with Windows OS. But there are many other ones – Google Chrome, Mozilla Firefox, Opera, etc. Editing can be done in in notepad or in Notepad++, which automatically completes individual tags or PSPad Editor.
You don´t need any other application for browsing HTML files. Right now you are using one. For editing you can use Notepad++.