There is no rocket science, it’s quite easy.
Be sure that all your computers are in the same WORKGROUP.
To change the WORKGROUP name type “my computer” in Windows 10, right click on the icon and click on properties. Then on remote settings and then on computer name.
Click there on “change” and type the name of the workgroup that should be similar on all your computers, Windows XP, 7 or 10. By default, it should be “MSHOME” with caps.
Now open windows explorer and go to network. The computers in your network should be listed there and you should be able to access the files and folders that are shared.
Be sure to have the files and folders shared from Windows XP.
To share from Windows 10, you also need to do some tweaks. Type “network” in the search bar and it should open network and sharing settings. From the left side click on “change advanced sharing settings. Turn on all the options there.
To share a folder then, right click on the folder, properties, security. Edit > add. Type “Everyone” and apply. From the bottom of the same window enable all permissions there.