please can you tell me what is HTML code editor
A basic code editor, not just for HTML but even other languages, is simply a text editor like Notepad in Windows but there are many more advanced editors with features like syntax highlighting, auto-complete, etc.. where you can edit the source code of an HTML document. When you view a web page in your browser, it "translates" the code into a visual page. To change how this page is displayed (or make a new one), you have to use a code editor.
sublime text editor ; hands down the best code editor available
notepad++ is really easy to use. Personally I use Brackets. there is aptana also, that's quite popular. any of these are code editor, some are just more fancy than others. please don't use Microsoft Word. that is not an editor.