Claims allow you to protect your land, builds, and chests. Claims cover all y-levels. You could claim land according to how many claim blocks you have. You gain approximately 150 claim blocks per hour of active play, through rares that give claim blocks, or they could be purchased on the Applecraft store.
As per the server rules, do not build or claim within 100 blocks or the range of another player.
To view your claims and available claimblocks, type /claimlist.
To claim land, you need a golden shovel. Claiming land is simple: right-click the ground in two opposite corners to claim your land. Claims must have an area of at least 100 blocks.