To label a file, drag a file or a folder to a label. Alternately, drag a label onto a file or folder.
To diff two file revisions: drop a file or a file revision onto another file revision. To display file revisions, context-click the file and choose Revision History.
To diff revisions of different files, display the Revision History window for both files, then drag a revision from one window to the other and drop it on the other revision.
To add files to a pending changelist, drop files onto the Files field of the pending changelist's Submit form.
To move a file from one changelist to another, drag files from the source Submit form to the target Submit form. Alternately, choose View>Pending Changelists, and drag the files from the source changelist to the target changelist.
To filter the pending changelists or submitted changelists displayed in the Specs pane, drag files or folders from the Tree pane to the filters field above the changelist pane.