Open a text editor and Chrome and Firefox browsers (or other browsers you prefer). Practice in the editor, save files as html, and open the files in Chrome and Firefox.
Practice getting pages to look the way you want in multiple browsers, take note of any differences between browsers and research how to tweak the html to fix any problems.
To publish your pages on the net, you'll have to get them hosted on a web server. But you can practice all you want offline, with the files stored locally.