Adding IP Address Aggregates
In the standard IPAM page - you should have an option to "Add Aggregate"
Once clicked, you should get a more detailed screen to add an aggregate block
When a block is added, you will be able to see it on the IPAM page
Architecting IP Address Blocks
Splitting blocks manually
Splitting blocks with Templates
IP Block parameters
Editing Attributes
Assigning IP Space
IPAM Gadget
Subnet vs Subassignment