How do I view all available HDD's/partitions?

There are many ways but my favorite is lsblk. Here is a demonstration:

sudo lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL

That would show the following:

NAME   FSTYPE   SIZE MOUNTPOINT LABEL
sda           111.8G            
├─sda1 swap     121M [SWAP]     
└─sda2 ext4   111.7G /          
sdb             2.7T            
└─sdb1 ext4     2.7T            xtreme
sdc             3.7T            
└─sdc1 ext4     3.7T            titan

It is showing:

• The name of the drive and the partitions it has.
• The type of file system.
• The size the whole drive has and the size each partition has.
• The mount point and if available, the label for them.

You can play around with the options by first looking at the ones available with lsblk --help. I like lsblk because of the friendly way of showing the information if compared for example with fdisk or parted.

The command-line solution:

• to check which drives your system can see:

  sudo fdisk -l
  

If your drive is in the list, you'll be able to see what partitions are on the drive, like this:

Disk /dev/sda: 160.0 GB, 160041885696 bytes
...

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          63      208844      104391   83  Linux
/dev/sda2          208845     2313359     1052257+  82  Linux swap / Solaris
/dev/sda3         2313360   312576704   155131672+  83  Linux

Then create a directory somewhere and mount one of the partitions. For example, to mount a FAT32 partition located at dev/sda3 read-only into directory /media/my_test_mount you can do

sudo mount -t cifs -o ro /dev/sda3 /media/my_test_mount

This approach gives you more control, as you can use different mount options, for example mount the partition read-only.

See man mount for details.

I second Luis in that lsblk(8) is probably the most straightforward and concise solution. It's very easy to visualize what is there and gives you all of the information needed quickly:

sudo lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL

For your convenience, here is a list of all available columns that can be used.

Available columns:
       NAME  device name
      KNAME  internal kernel device name
    MAJ:MIN  major:minor device number
     FSTYPE  filesystem type
 MOUNTPOINT  where the device is mounted
      LABEL  filesystem LABEL
       UUID  filesystem UUID
         RO  read-only device
         RM  removable device
      MODEL  device identifier
       SIZE  size of the device
      STATE  state of the device
      OWNER  user name
      GROUP  group name
       MODE  device node permissions
  ALIGNMENT  alignment offset
     MIN-IO  minimum I/O size
     OPT-IO  optimal I/O size
    PHY-SEC  physical sector size
    LOG-SEC  logical sector size
       ROTA  rotational device
      SCHED  I/O scheduler name
    RQ-SIZE  request queue size
       TYPE  device type
   DISC-ALN  discard alignment offset
  DISC-GRAN  discard granularity
   DISC-MAX  discard max bytes
  DISC-ZERO  discard zeroes data