HTML is a Hypertext Markup Language; it's a Predominant set of Markup tags which used to create design of web pages. HTML is relatively easy to learn, because every tag is predefined so only we need to know the work of tags and its attributes. Web browsers (Chrome, Internet Explorer, Firefox, Safari) is software’s for reading HTML and to display webpage design as output.
We can write HTML in any simple editor like Notepad. Professionally Adobe Dreamweaver is used for, HTML writing and editing. If you are not using Windows, you can use a similar simple text editor. For example, Pico (Linux) or TextEdit (Mac).
.html extension is used for writing HTML file, so we can write HTML code in any editor, and can save as filename.html.