Land Claiming / Flan
On the A Realm Recrafted SMP Server claims are pieces of land with restricted permissions to prevent griefing with a depth of 32 which means they extend 32 blocks downwards from the claiming spot but no limit upwards. This makes it so it wont affect mining below claims but claims will extend if players start building below. They support subclaims to create town like systems where subclaims have their own permissions too. Being in SubClaim-Mode allows you to edit subclaims.
How To
To get started the first thing you need is a golden hoe. This will be your tool to create land claims. Holding the tool will display your current claim blocks and the amount you used.
To create a claim now right click on one block to select a corner and on another block to set the other corner. If it was successful you will get a message that a claim was created, else it will tell you why the creation failed. Alternatively you can also use the command /flan addClaim to do that if by some reason you prefer that method.
Resizing claim is done by right clicking on one corner of a claim and then on another block to set the new corner. To check if a block is claimed you can use the inspect tool (Stick).
Standing in a claim and typing /flan menu a gui will open to help you customize your claim further.
Additional Infos
If you need any further help with claiming your land, than you can check out the Mod Authors wiki for a detailed overview: Flan Wiki