Lost Storage

I just purchased a WDBACW0010HBK-NESN external hard drive. According to my computer I have only 112GB free space left for storage(out of 931.5GB). Under the heading “Additional Files”, it states that I have used up 819.5GB of storage space. I don’t know how this can be possible. My computer does not have a great deal of data on it and as I just stated, the product was just purchased recently. The drive had a great deal of storage remaining at one point. It then seemingly jumped to having a great deal of storage used and little room for additional storage to be used. Could my files somehow have been backed up repeatedly by mistake and taken up all this space? I am not very computer savvy and I have no clue what to do. The salesperson seemed to think that this hard drive would last an average computer user, such as myself, a very long time. Please help.

In this case there could be several reasons:

1- Indeed, you could have several copies of the same files, in order to find you you can access the drive root folder and verify the files names.

2- You could have some unallocated space, go to disk management and verify if your drive has any unallocated space.