Using Repetier Host, I slice the item and go to the Print Preview tab and click the Save for SD Print box. This allows me to save the file on my laptop. Then when I go to the SD Card tab, the file does not appear on the file list. So I need to somehow move the file from my laptop to the list so I can upload to the SD card. That must be very straight forward but I just don't see how to do this.
If anyone can give me a clue, I would appreciate it. Thanks.

Got it. Thanks.

in repetier host you have menus top left one of them is printer and in it is the sd card manager look around at that and also the G code Editor icons one allows you to save the Gcode. I never use the SD card as most of my prints are done once and if I do print again it may be with a different filament and temperature in which case you need to re slice. I keep all stl files and associated cad on USB sticks and print from laptop. Make sure a valid SD card is being used as some have different formats