Please follow the instructions below carefully.
1. Go to Disk Utilities
Shift + Command + U and open Disk Utilities
2. Click the Hardrive you want to partition.
3. Click Partition tab.
4. Click + sign depends on how many partitions you want to create.
5. You may change the name or size to adjust the partition.
6. Once you’ve done, click apply, wait then you’re done.