In most graphical desktop environments, Emacs has basic support for drag and drop operations. For instance, dropping text onto an Emacs frame inserts the text where it is dropped. Dropping a file onto an Emacs frame visits that file. As a special case, dropping the file on a Dired buffer moves or copies the file (according to the conventions of the application it came from) into the directory displayed in that buffer.
Dropping a file normally visits it in the window you drop it on. If you prefer to visit the file in a new window in such cases, customize the variable dnd-open-file-other-window.
The XDND and Motif drag and drop protocols, and the old KDE 1.x protocol, are currently supported.