You need first, to mount the partitions on second drive somewhere in your system.
After that is a matter of copy-paste.
To know what are the partitions on the second drive, as root (superuser), "fdisk -l". This command will list all disks and all partitions and types woy may have.
After that, use the command mount to mount a selected partition on a arbitrary mount point. Let say, your second disk is named /dev/hdb and it has 2 primary partitions and you want to mount the second one on /mnt/personal, in read-only mode, just to avoid the risk of any mess:
# mkdir /mnt/personal
# mount /dev/hdb2 /mnt/personal -o ro
# ls /mnt/personal
you should see the files on that partition here...
After that, open you favorite filemanager, point it to /mnt/personal select/copy the files, open a second filemanager, point it to destination, and paste.