Normal Ranks are levels from 0 to 20. ①②③⑳
Extended Ranks go beyond 20 and are mostly a sign of how much you have played, they don’t offer many bonuses.
Everybody starts at rank 0 and will automatically rank up after completing certain requirements.
Requirements include: time played, skill levels, achievements, fishing.
There is also a quiz to reach levels 4, 9, 14 and 19.

To view the requirements to reach your next rank, type:

Completed tasks will be green, incomplete tasks will be red.

Once you have completed all of the tasks, you will either need to log out and in to rank up, or just type:
/rank check

When you are ready to take a quiz, type:
/rank quiz

To keep track of the fishing requirements, you can check which fish you have caught by typing:

Reaching rank 20 is not an easy task.

Players can also donate to reach a higher rank level. Although, to level up you will still need to complete all of the lower rank requirements.
For example, an Ender donator will start on rank 16, but to get to 17 they will need to complete all of the requirements for ranks 1-16 as well.

The highest rank you can achieve through donating is 20.
If you are interested in donating, click here.