Here's how to add HTML to your site using the HTML Code Widget:

1. Click on Widgets > Popular.
2. Drag and drop the HTML Code Widget onto the page.
3. The HTML Editor will open up allowing you to write or paste your code (use right-click > paste or Ctrl-V to paste).
4. When you are done, click "Save". 

Here's how to add HTML to your site using the Text Widget:

1. Click the HTML button on the Text EditingToolbar.
2. Edit the HTML as desired.
3. When you are finished, click "OK" to return to editing text with the Text Editing Toolbar.

If you are editing a blog post, you can insert custom HTML, using the HTML button on the blog Text Editing Toolbar (works the same as a Text Widget).