Hold down the Windows key, and press R. Type "diskpart" into the box. This will launch the command line partitioning tool. Type "list disk" and see what it spits out. Note which drive is the one you want to work with.
Now type "select disk #", where # is the number of the disk you want. Now type "clean" to wipe whatever partition table it has already.
Now enter "create partition primary", which will create a single partition the size of the whole drive. All that's left now is to format it with "format fs=ntfs label=PartitionName", where PartitionName can be whatever you want.
That might take a while, so go make a coffee or something.
Once that's done, type "assign letter=G" or whatever letter you want assigned to the partition, and you should get a popup from Windows asking what you want to do with the new partition.