Hello Earthworm Jim,
Welcome to Apple Discussions!
If you are wanting to actually print the window of app to printer, then command+P.
If you are trying to get a screen shot, then here are a few hints.
The result of the following will be a PNG on the desktop, unless you change the default locations and file type.
1. To capture entire screen:
CmdShift3
2. To get a screen shot of just a selected area:
*Cmd
Shift4 then highlight wanted area with mouse*.
3. To copy to the clipboard so you can paste into a document: (this is probably the one you are wanting)
CtrlCommandShift-3(or4)
Also you can use the GRAB app in Utilities, which will also capture the mouse pointer and save as TIFF.
Message was edited by: iyacyas