To edit the html code of a CMS page, go to Tools and then selecting CMS - Page Editor.

Then Select a page to edit, by clicking on the required "edit" icon under status

Once in the editor you can then click on the source button  this will turn the editor into html mode. You can then add your required html to the appropriate section. Then click on the source button again to switch to wysiwyg mode and click on the save button.