First, create a Blogger Accordion widget on Common Ninja.
On the widgets catalog, find the Accordion and enter the Editor.
When you're done creating the Accordion widget, click on the Save Changes button at the right top corner of the editor.
If you don't have an account on Common Ninja, you'll have to register first.
When you're ready to add the Accordion widget to your Blogger website, click the Add To Website button at the top bar of the Editor.
On the window that opens, click the Copy Icon to copy the widget embed code. In the next steps, you will paste this code into your Blogger website.
Now, let's head to your Blogger website editor.
In the Blogger editor, select a page or a post you wish to add the Accordion.
Click the Compose View button at the left top corner of the screen.
Under the Compose View button, select the HTML View.
Now, in the HTML code of the page, simply paste the Accordion embed code, wherever you wish the Accordion to show.
Switch back to Compose view by selecting it on the top left corner of the screen.
Click the Update button at the top right corner of the screen, to save your changes.
Please note: the Accordion's content will only show on the preview and on the published site.