you need a up running system

it can be another windows, that you hook the disk to be partitioned on.

Or, it can be the installation environment of Windows. During installation the disc can be partitioned. However, suggest to have only the first one partitioned and leave the empty space for after windows is up. Otherwise the remaining partitions will be created as "secondary" and "logic dick" which is not easy to use. I like "primary" partitions!

Another way is to use Linux-Live and run fdisk, cfdisk ...