Ah, Winstar... They supply woeful data if you could call what they do give you data. Also, be careful with them as they will change the controller IC and not tell you . You can't tell it has been changed under the black gunk they put over them. You end up really pissed off after you've just had 500 of them loaded onto boards and discover that there was a subtle timing change in the controller which means that none of the 500 boards you've just had made work.
To make matters worse, they won't be able to tell you what has changed in the controller and after you spend a week pulling your hair out you decide that they are just faulty and start the re-work process. Winstar won't supply you replacements until you return the crook ones to them and they won't help share any of your re-work costs either.
You have been warned !
Now to your questions.
DDRAM is Display Data RAM - what ends up on the display
CGRAM is Character Generator RAM - Allows you to build a few custom display characters in the LCD module. This is normally only found in Text mode LCD's. As your display is a pure graphic display, it shouldn't have any CGRAM
Using LCD's is pretty straight forward. This one looks as though it uses a Samsung KS0107 controller, so search for a datasheet for that component and you should be able to get all of the info you need. But, once again - remember that Winstar can change controllers without warning.
If you don't know where to start with controlling LCD's, that is a little beyond the scope of a quick message.
Instead, I suggest you have a look
HERE and
HERE .
I only gave each site a quick glimpse but they seems to be basically what you might be after.