The title says it. What is the procedure to make screen shots to share from these games?

There is no ingame screenshot feature in these games. You need to use third party programs like fraps, snagit, or snipping tool.
I prefer using IrfanView, which is basically an image processing software, but it has a powerful screen capture tool. You can choose from a variety of formats to save your shots. It also has a very good batch processing feature which allows you to transform lots of screenshots into a different format or size.

There is a list on Wikipedia:
http://en.wikipedia.org/wiki/Comparison_of_screencasting_software

Sadly, the above list is missing IrfanView:
http://en.wikipedia.org/wiki/Irfanview

Almost forgot: I believe these games are run in DosBox by default, which has it's own screenshot feature. Ctrl-F5 should make a screenshot and store it in the DosBox capture folder. But I'm not sure if and how GOG has configured this inbuilt feature.

You can take a screenshot by pressing "Prt Scr" i.e. the "Print Screen" key on your keyboard. Then you can Alt-Tab out of the game, open up mspaint and paste from the clipboard to create the image file.

Also note that the above works for just about any program in Windows, including desktop screenshots. MM6 - MM8 are windows-based and don't run with DOSBox.

Thank you both for the answers. I wound up doing it rmeakins' way. I pressed "print screen" to the Windows clipboard, and pasted into Paint.net.