Simply you can run .html file in your own browser..html is an extension of a html file.As well as you could use .htm too.On older web pages you may see .htm, but this archaic and no longer used.A file extension or file name extension is the ending of a file that helps identify the type of file in operating systems.
Windows 7 or earlier:
Click on the Start button to open the Start menu.Here you can type notepad or
you'll have to click on All Programs.
then click on Accessories and then on Notepad
Windows 8 or later:
Open the Start Screen (the window symbol at the bottom left on your screen). Type Notepad.
MAC:
Open Finder > Applications > TextEdit
Also change some preferences to get the application to save files correctly. In Preferences > Format > choose "Plain Text"
Then under "Open and Save", check the box that says "Ignore rich text commands in HTML files".
Then open a new document to place the code.
<!DOCTYPE html>
<html>
<head>
<title>My First Web Page!</title>
</head>
<body>
<h1>Hello World!</h1>
</body>
</html>
you just write your html file inside of your text editor.you didn't save it.so you have to save it to make it any use
To save select File > Save as in the Notepad menu.
name it with the extension .html i.e. your_file_name.html
Note:Don't use any spaces or special characters in the file name. Use underscores (_) or dashes (-) instead.
Open the saved HTML file in your favorite browser (double click on the file, or right-click - and choose "Open with").