As noted in the Intro page for Accordions, each row in the accordion is simply an Article assigned to a pre-chosen Category.
So what you're seeing when you view an accordion is a list of articles in the same category, displayed in away so they expand and contract when you click them.
What to do
Go to Content > Articles and click the New button top left.
Give the article a suitable title. This is the text that will be displayed as the accordion row title so make it nice and tidy!
In the right hand panel, look for the Category chooser dropdown and use it to select the correct category for your new accordion row. So, if your accordion is aboutthe Year Group Curriculum, choose the accoridon that relates to that subject
Often the Category will have the text (Accordion) as part of the category name
Once the category is selected correctly, you can populate the body of the article with the most appropriate content for the accordion.