Nobling means taking over another village. It is the only way to get to a second village. To noble a village, you first need a nobleman and attack the target with it. In a successful attack, the nobleman reduces the village's loyalty. The base loyalty of a village is 100 and every attack lowers the loyalty by 20-35, even if you send more than one nobleman in that attack. To take over the village the loyalty needs to take down to 0 or lower. This usually takes 4 or 5 attacks, in rare cases, it can also be done with 3 attacks.
A nobleman attacking alone usually dies on the base defense of a village so you should always send troops with it.
As soon as the nobleman has lowered the loyalty to 0 or less, it takes over the reign of the village and cannot be used for another attack.