These would be Internal. Internal SATA (aka - mechanical drives) Typically have two cables 1 Power - 2. Data.

Are you wanting space on your Primary Drive → C:

If so you would have to reinstall your Operating System replacing that one. Some people might just copy and paste however I can not recommend that.

The instillation process can be found on you tube. It will ideinfy the two cables (Power and Data) showing you where to plug them in. However if you have multiple internal drives and not sure what your doing - I would say wait until your son is able to help.
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On the other Hand ... if your happy just to use an external drive for your storage space (photos, videos, documents, Software Install files, and other programs) and not use it to run programs from ... then leave me it to me and I will link the best budget ones I would choose.

You said your desktop space? ... so I am now wondering was it your internal primary drive or may an internal secondary/storage drive ... or you just looking to upgrade an external usb drive to allow for my file space?