If you’re wanting to know general commands, type /basics claiming in game to learn those and what they do!
First, while holding your golden shovel in your hand, you put the shovel into subdivision mode with the command /subdivideclaim.
Now you right click the shovel at one corner of the area you wish to subdivide, and again at the opposite corner (as if you were making a new claim around it, note that subdividing a claim does not use any additional claim blocks) You will then see the area outlined in wool and iron blocks.
When you have the area subdivided, you simply stand inside it and can use /trust, /accesstrust, /containertrust and /permissiontrust as if you were trusting someone in a full claim.
If you trust someone within one of your subdivisions, they will only be able to build/access containers in that subdivision. Or if you have subdivisions on a claim and /trust someone outside of the subdivision they can build everywhere but the subdivisions.
To remove the subdivision: stand inside the sub claim and type /abandonbandonclaim as normal. You can’t remove the larger main claim when it’s subdivided with the /abandonclaim command. If you want to delete the main claim the command changes to /abandontoplevelclaim which deletes the main claim and all subdivisions.
For a basic tutorial on how to claim, you can watch this video: