If you have a My Cloud Home, you will need your friends username and password to access the content in their User Private Space or access the Public Share in macOS Finder or Windows Networking.
If your has a My Cloud Home, your friend may have added you as a guest user.
You will not see his content as a guest user unless he puts the content in the Family Folder.
If he put the content in the Public share, you will not see it remotely, only using the Local LAN