You can apply for two types of nobility: IG nobility and RP nobility.
IG nobility is the one you obtain purchasing credits with real money on the RK shop website. In change of credits you can buy low or high IG noble status with some play advantages for twenty days: you will have a horse (three nodes a day); you have a reserved seat in taverns (unless there is another noble on it); you study faster on level 3; your Town Hall will be given a small daily amount of money for your stay in town. Past the twenty days you'll have to use again one or two credits for another 20 days of nobility.
Then we have RP nobility. For special merits, long and distinguished career, war bravery, you can obtain from the Royal Honours Authority (England) or Lyons Court of Arms (Scotland) a title such as Lord, or Marquis, or Viscount and so on, with a coat of arms, fields and pertinences.