The user can create single Filters and Value Fields using the Meta data field or Table and column tabs in the Add view. It is also possible to create a filter Group. However, a search can be extremely flexible: filters in value fields, bind fields, groups within groups, and many other possibilities. For now, disregard these extraordinary features, because they will normally not be needed and are not documented.
The Predefined tab in the Add view enables creation of elements, which the UI does not necessarily support editing or displaying of.
For example:
Creating a value field with a bind field and several filters
How to create a predefined value field.
The Details panel displays an uneditable text field; this is used whenever an element cannot be parsed correctly by the UI. This is not an error: a search theoretically supports infinite nesting of filters/value fields and so a choice was made not to support displaying and editing elements, which have nested filters or value fields.
In other words, be wary of using predefined elements because they might be overly complex and offer a lot less transparency.