Selecting this menu item saves the active visualization window to a file. The saved format depends on what you specified via the Set save options window.
The active visualization window is the window listed beside the Active window label in the MeshTV Main window. Windows are numbered consecutively between 1 and 16, inclusive.
Note that if the Screen capture toggle button is on, you need to make sure that you have no windows obscuring your plots, since these will show up in the saved image. You can check the values of various save options by selecting the Set save options... menu item from the File menu.