How do I insert HTML into the home page and content pages?
In order to insert HTML into the homepage and content pages, you will need to click the "Source" button in the WYSIWYG editor. Then you can type in or paste your HTML. If you add in <style> tags while in source mode, you can also add in specific CSS just for that homepage or content page.
If you wish to always use HTML and to disable the WYSIWYG editors, you can do that under Settings > Store Settings.