How to create post template in Wordpress

I must have deleted something - I’ve got a Single Post Template in my website and have posts using it etc… but I made them originally in Wordpress. Now I can’t find how I entered them into Wordpress. I think I just used the “Standard” template but now it just has a title in it when I click “Add New Post”. Where do I edit that “Standard” template?

Hi Grant,
If you have a custom template for your single posts, please ensure it contains a “Post content” element with source “WordPress”.

Please provide a screencast showing your setup/problem if it still does not work.

Best regards,
timmse