First time set up of new laptop samsung r530. Set-up asking what I want to set the c-drive and d-drive at...showing a slide rule..it's at fifty-fifty on the screen. Should I change it or leave as it is? Many thanks.

Its completely up to you, if your documents folder is in the D: drive, i would set the D: at about 200GB. If the D: drive is just free space I would set the C: drive at about 250GB. as this would hold your program files and your documents

I am assuming it is just splitting up the hard drive into 2 drives. Depending on how your gonna use it most likely you can just leave it where it is as there isn't really a reason to change it one way or another for the average user.
Thanks,
Lee