macOS Disk Utility allows you to view, modify, create & delete existing APFS partitions while inside macOS.
How to access Disk Utility
In your menu bar
1. Open Spotlight Search
2. Type in Disk Utility & select it
How to create an APFS partition and view existing partitions.
When in Disk Utility
1. Right-click on the Volume you want to create an APFS partition in
2. Select "Add APFS volume"
3. Name your APFS partition
4. Select Size Options & allocate space for this APFS partition.
1. Note - as stated in the Size Options pane, the Reserve size ensures the inputted amount of storage stays in the original Volume. While the Quota size is the amount allocated to the new APFS partition.
2. As pictured below, our Quota size is 500 MB, and I've left the Reserve Size empty.
3. Click "OK", then select "Add"
1. Note this process can take minutes or hours - depending on the APFS partition size.
When the process completes, it'll look like this:
4. You can now select your new APFS partition on the left list.
You've now created an APFS partition.
How to delete an APFS partition
1. Follow the previous steps to access Disk Utility.
2. In the left list, select the partition you want to delete & right click on it
3. Select Delete APFS
4. Select Delete & let it process
4.1 Note this process can also take quite a while - depending on the size of the APFS partition.