- The 2 computers need to have the same 'workgroup' (not necessarily ABC, there's nothing wrong with the standard WORKGROUP, I think), but a different name (not necessarily A and B, there's nothing wrong with calling them WIN7 and WIN10.
- To share data in a network it's best to have the same userid with the same password on both PC's.
- For the copy you can either (1) login to the WIN7 and connect to WIN10 and then copy from c: to the drive letter the WIN10 gets, or (2) login to WIN10 and then copy from the drive letter the WIN7 gets to the c:. You need to enable file sharing on the computer you're not logged into to, with the right permissions (write in case 1, or read in case 2).
Although here I do it by connecting both PC's via an Ethernet switch, the direct cable should work also.