I've inherited a Leica Stemar kit with the matching leitz stereo projector but I have no idea how to use it. Does the projection of stereo slide require some kind of stereo glasses or background to get the effect? Is there anyone with experience on this equipment?
I don’t have experience with that kit but I do shoot View-Master stereo slides and view them with a projector. The View-Master projector uses polarizing filters to separate the images so you need to wear polarizing stereo glasses. The other way to view projected stereo slides is with blue and red filters in which case you would wear red/blue glasses. You need to check what filters are in the projector. If it has polarizing filters you will need a silver coated screen to view it, white screens don’t work well with polarizers.
At one time I was keen on getting a Leica stereo outfit, but just as with the attachments made by Zeiss and others, stereo photos are in portrait format only. You did luck out because there is collector interest. You can do very well when selling.
As for 3D photography, you would do better, and cheaper, with Stereo Realist camera.