Select the graph by clicking the graph or the cell, then select File ▶ Save Selection As. In the Save As dialog box, select the file type in the Save as type: dropdown menu. Here, the graphic is saved as a JPEG:
With the graphic selected, use either the Edit ▶ Copy menu item, the Ctrl+ C (PC) or Cmd+ C (Macintosh) keyboard shortcuts, or Copy Graphic from the contextual menu that appears after right-clicking the graphic.
You can also use Export to export a graphic. Export a graph of as a JPEG: