Activate drag and drop

I don't think there's anything special you need to do to activate drag-and-drop.

In contexts that support it, you

• Use the mouse to select an item or items
• Left-click on one of the selected items – and keep the left mouse button held down
• While keeping the left mouse button held down, drag the pointer to the destination area
• Release the left mouse button

Whether this results in displaying the contents of the item depends on the context. For instance, if you were dragging and dropping files from one disk to another, to copy them, that normally would not open the files for viewing or editing.