Answer:   Whenever we click on a tab or we click on a lookup icon or search for a record we see only one standard field by default, to enable remaining fields –
• To show multiple fields for the records which display under a tab, on object detail page > under Search layouts edit tab and add required fields.
• To show multiple fields for the records which display when we click on lookup of a field, on object detail page > under Search layouts edit Lookup Dialogs and add required fields.
• To show multiple fields for the records which display when we search for the records, on object detail page > under Search layouts edit Search Results and add required fields.