Someone online explained it well:
Drive manufacturers report drive sizes using base 10 math while computer operating systems tend to report these sizes using base 2 math. The advantage of using base 2 math means that the code is somewhat simpler and it will run faster.
Basically, A drive that is marketed as 1 TB (1,000GB) assumes that 1,000 Kilobytes make up 1 Megabyte. But in actuality, Windows allocates 1,024 Kilobytes to 1 Megabyte. When you do the math on this, a 1TB hard drive ends up showing as ~931GB. This is normal.
All partitions are logical partitions as far as the operating system is concerned. a Primary partition is bootable.
You have to format the partition. I believe the program I mentioned does this for you. You want to format it as NTFS. You can give the partition a name though I think this is optional.