In the Monaco editor, you write the Liquid Syntax (base for Display Pattern) in the Monaco editor.
The search and paging to find a specific item you want to see in the preview. To find a specific content item search for the content's id which is shown in the content detail view URL bar e.g. id:cb20faba4e3342d9a9f83191deeec115
The preview will give you a preview of the Display Pattern (you must have at least one content item filled out with the values in the Display Pattern for a preview to display).
You can add fields of the schema easily by clicking on them. Each field will be added with a liquid tag checking if the field is not empty and the liquid object which is the field.
Layers are only necessary for the Virtual Type Display Pattern. The fields will be the virtual type fields and additional metadata fields from layers will be available in this section.
Languages allow you to add a different Display Pattern per Metadata language. If you only update the default language this will be used in all other languages, the values are always translated if translations are available.
Hint: Adding languages makes only sense if you use static text in the Display Pattern which then not be translated.
The JSON preview shows the detailed data structure of the current item you are previewing and all the available objects you have for the Display Pattern.
You can use this for debugging or to check which fields are available for usage.
In contentSchemaId – you find data – where you find all metadata you can use e.g. the title which is translated into en only.