Mount drives

If disk is already formatted, You can mount it. You may need to create a file system for it though. 
If you do, Replace 
XY accordingly, but double check that you are specifying the correct partition
mkfs.ext4 /dev/sdXY
Do that to all the drives/partitions you need to.
Now you should be able to go to "Disk manager" in the GUI or, mount the drive/s manually. 
To mount in Terminal:
create a mount point (if you haven't already)
sudo mkdir /directry/to/mount/to
Now mount it:
mount /dev/sbxy /new/mounted/location
 
Check your file type before you continue
lsblk -f 
If you want it permanent, you will need to add it to the fstab. 
Mounting from fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# /this uses the UUID of the drive and mounts it do the directory you want it to go to
UUID=57sdfgsdf4jk-f2nh-49u8-9596-719a26547f94 /mount/dir  ext4    errors=remount-ro 0 0
# /this uses the drive location and mounts it to the directory 
/dev/sdb /mount/dir  ext4    errors=remount-ro 0 0
Type "lsblk" is your drive mounted?
Type "sudo mount -a"   How about now? 
Try "lsblk" again.