Is there a video that shows how to set up a single field as editable from the online editor?

I thought I would start simple with the CMS but it’s defeating me at the moment. I’ve added a CMS page with the online editor, logged on to that and created a single markdown file containing text and saved that but with everything I’ve tried so far I’ve not been able to link to that file to an Item on my Home page to show the CMS controlled text on my Home page. Is there an idiots guide somewhere on how to do this please?