You are now creating the caption of a Picture of the day. The caption will be used for example on the main page of the specified language. Please check that you are creating the right page. The name of this page should be Template:Potd/YYYY-MM-DD (xx), where xx is the language code for the specified language, YYYY year, MM month and DD day. The language code of English is en. You are now creating a page named Template:CreatePotdDescription.
Add the following syntax to the edit window and replace Caption with your caption, YYYY with year, MM with month, DD with day and xx with the language code of the specified language.
After you have written your caption, preview this page. It should look like this page, but with different caption and image. After you have previewed this page, you can save it. Thank you for your help.