Detected means the system sees them. Mounted means the partitions in those drives have been mapped to a local area on your filesystem where you can access them.

Depending on your desktop and settings, this is usually an automatic thing for well known filesystems like NTFS or FAT, but not so with encrypted volumes because there are extra steps to mounting them during boot (like a passphrase).

If they you had Bitlocker enabled in Windows, then they will not automount. So if in Gnome open up the 'Disks' app, or 'Partition Manager' in KDE, see if your dicks show up there, then click on the partition you want to mount and it should ask for your disk password to mount it.