If you have a test system, that would be great to work with, or download the NetApp VSIM to do some exercises with this. Basically, the aggregate create and aggregate add command automatically handle creating raid groups. The default raid group size for dual parity with SATA is 14 and 16 with FC/SAS.. So for example, if you create an aggregate with 32 600GB SAS drives, ONTAP will automatically create 2 raid groups of 16. If you then add 10 more drives (best practice is a full raid group at a time though) it will automatically create a new 3rd raid group with those 10 drives. Then if you add 22 more, it will fill out the 3rd raid group to 16 (from 10) and create a 4th raid group of 16 automatically. You can also change the default raid size and also add drives manually to existing raid groups, or force creation of a new raid group. ONTAP is flexible to do almost anything you want (within the aggr and rg size limits) but the automatic volume management to create new raid groups works well.
You could test with both System Manager (GUI) and the command line "aggr create" and "agg add" command to learn the syntax. Some only use System Manager which works well, but if you want to do some things like add to an existing raid group, learning the cli is good to know.
