How did my 2TB Passport get partitioned without my help?

I am a newby. I am using Win 10 Home (build 18362). I have a tangental question, to backups: I bgt. my 2TB HD (My Passport), 3 months ago. use it to store tv shows. When I plug it in to my Surface tablet and open File Explorer, it reads 4 items: all NTFS system (i) My Passport D (ii) local disc E (iii) local disc F. (iv) Local disc H. When I click on Properties for My Passport D it shows used space 139GB and unused space 29GB (total 160GB). In each of the other 3 locations, (E,F,H ) Properties shows unused space, of 699GB.
Obviously, I can copy/safe my data and then format the drirve. My question is, what did I do wrong to create this situation, so I can avoid it in future, please?. Thanks! Don PS: I used disk management function to delete/un-allocate the volumes. Now I have a HD that does not have an identity, so it is not accessible using File Explorer.

Please ignore my post. I have now learned how to use File Management. I restored my Passport HD to its original state; i.e. simple layout, all of the volume is in a Primary Partition and it has an indentifying letter (D).
hope i didn’t waste anyone’s time.