If it's brand new, you may need to initialize, partition, and add a file system to make it ready for data
So, plug it into a USB 3 or 2 plug, boot up your computer, and then go to Disk Management. In the lower graphical section, you should see the drive listed as Disk 1 or Disk 2. There are two sections to this area, the DriveStatus area where the Disk 1 is listed, and the VolumeStatus area where the partitions and file system are listed.
If it says Initialize, go ahead and do that choosing the Basic style, and probably make 1 large 500GB partition (or a couple smaller partitions if you want) using MBR if asked. That also places a disk signature on the drive. Then you can Full Format the partition making it ready for data using NTFS and the default 4k allocation units. Takes a while.
When done, you can assign a drive letter to the partition, like 'K' for back up, or whatever, and by clicking on Properties, can give it a VolumeName, like 'BackUp Drive' your choice. Once the letter is assigned, it will be recognized in Windows Explorer.