Hi Elizabeth,
My name is Lee and I'll be happy to help.
Drive D:\ and External Drives can be found in File Explorer. Right click the Window icon on the bottom left and select File Explorer then click This PC. If Drive D:\ is not there, most probably you haven't partition your hard drive and to partition the Hard drive you can do that in Disk Management.
Here is a very helpful YouTube video that that you can follow to create a drive D:
https://www.youtube.com/watch?v=wQQ-ohOdcZU
~ Lee
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