Hey there, Smithy07.
Don't worry for being new to this field. Everybody has to start from somewhere.
You can use a 128GB drive for your OS (operating system, which is Windows in your case) along with a 4TB drive for simple storage and games. This is a actually a pretty good combo.
My recommendation is that you install the OS on the SSD without having the HDD connected to the motherboard during the Windows installation process. This is necessary because Windows sometimes puts some of the system files on the secondary storage HDD and by having it disconnected during the Windows installation, you will prevent future possible issues while booting or updating the OS.
I'd advise you to use the SSD for the programs as well (not the games just programs which are not too demanding it terms of capacity). You should also make sure that you set the SATA mode of your motherboard to AHCI before you start the Windows installation on your SSD. This is done via the BIOS/UEFI settings.
Here's a useful article with tips for new SSD users: https://www.maketecheasier.com/12-things-you-must-do-when-running-a-solid-state-drive-in-windows-7/.
Hope that helps. Don't hesitate to ask if you have any other questions whatsoever.
Boogieman_WD