A good handover lets a new editor publish an article and recover from an ordinary mistake. Focus the guide on the tasks they will do first.
Write out the steps to sign in, create a draft, choose a category, add a featured image and preview the post. Include a short example title and a screenshot of the relevant controls. Show how to update an existing post and locate a revision.
Test the instructions with someone who did not build the site. Ask them to create a sample draft and note where they get stuck. Keep account ownership and hosting contacts in a separate section for the administrator.