WARNING THIS WILL DELETE ALL FILES ON THE DRIVE. PLEASE BACK UP YOUR FILES BEFORE PROCEEDING.
There are a lot of benefits to making partitions on an installed drive but if you wish to extend this to your external drive here is how.
Press WINDOWS FLAG + R (RUN)
Type diskmgmt.msc press ENTER
You will be presented with the Disk Management Interface, be sure you select your External HDD (here it is My Passport)
Right click and delete the existing partition you should see that your whole drive has become un allocated space (black bar)
Right click again and choose New Partition… and follow the Wizard.
For storage we will be using Primary partition, hit Next
Select how much storage you will allocate for the 1st partition for this example I will create a 100Gb partition, type in the size and hit Next
I choose not to assign drive letter, hit Next
You may choose to Format the new partition here or later under Windows Explorer. For this tutorial we will format it as NTFS and name it MyBackup hit Next
You will be presented with a summary hit Finish to proceed or back to make more changes,
Now we can see a new partition and the space left as Unallocated (still black).
Repeat the steps to create more partitions.
Here I have created 2 partitions 1 named MyBackup the other named MyStorage.