Okay, before we start let me quickly explain something as it is needed to understand the advancement of rank. Some ranks requires missions and battles to advance. For battles, there are special rules in place:
➺ Lower and Higher Ranked Battles: Fighting a bio that is one rank below your own rank counts as .5 instead of 1. But on the other hand, a battle against somebody of higher rank will count as either 1.5 or 2 depending on if the their rank is only one above your own or more than one above.
This means, if you are Genin and you fight a Genin, it counts as 1 point. But if you are Genin and you fight an Academy Student (one rank lower than you) then it only counts as 0.5 points. Lastly, if you are a Genin and you fight a Chunin, it counts as 1.5 points as they are one rank higher than you. And lastly, if you are Genin and you fight a Jounin, it counts for 2 points as they are two ranks above you. That's the peak. These points come into play when ranking up. That means, when you have to get say 4 points to advance in rank, you'd need 4 fights (1+1+1+1) against people at equal rank, or 2 fights (2+2) against people of two ranks above you .
As for the ranks, there exists 5 different ones and they are as follow:
1. Academy Student:
This is the starting rank. When you make your first bio, you start here. You don't have to do anything to get it. At this rank, you have 300 chakra and 35 health. You have the ability to get 2 basic elements (from Fire, Wind, Earth, Water and Lightning) and 1 Basic Ninja Skill (from Genjutsu, Taijutsu, Ninjutsu and Kenjutsu). These can be up to C Rank and which means, you can submit up to C rank Custom Jutsu of those you picked.
2. Genin:
This is the second rank and the first one you achieve via something. In order to advance from Academy Student to Genin, you need to complete EITHER 4 D/C rank missions, OR 4 Battles against someone of the same rank as you (Genin) OR a combination of the two (2 missions and 2 battles, or 3 missions and 1 battle). Remember the point system I explained above? You would use that. With this rank, you get 600 Chakra and 75 Health, as well as access to 3 Basic Elements and 2 Basic Ninja Skill at B rank.. You also get to submit up to B rank Custom Jutsu of those you picked.
3. Chunin:
This is the third and basically mid way rank. To get to this rank from Genin rank, you have to complete 5 missions of B/A rank, or 5 battles (either against individuals at Chunin rank, or higher. If higher, then apply the point system explained above to get more points and thus, less fights) or a combination of the two. You gain 1000 Chakra and 100 Health points.. Now here things get a bit better. You have access to 4 Basic Elements at A rank and 4 Basic Ninja Skills at A rank. One of the elements can be chosen to go up to S rank. Lastly, you can submit up to A rank Custom Jutsu of those you picked.
4. Jounin:
The one I am at currently. To get this rank from Chunin rank you have to complete 6 missions of S rank or 6 battles against those of comparable rank or higher (only one higher at this point is Sages) or a combination of the two.. You get 1600 Chakra and 160 Health points as well as access to all 5 elements up S rank and above (Forbidden rank). This allows you to submit Custom Jutsu up to Forbidden Rank of all the elements you have at that point.
5. Sage:
The most difficult one and also for good reason. The Sage rank can be achieved through EITHER purchasing it for 25 000 Kumi or by completing a Sage Mission which is unique and given to you by LoK if you fit the requirements. Why is Sage so cool? You get 2000 Chakra and 200 Health as well as the ability to MAKE YOUR OWN CUSTOM CLAN. Not be confused with clans in the Ninja World/WSE, these custom clans are ones that you make with abilities and everything. Some examples include the Kisei clan (based on Harry Potter, clan members use wands and have a magic like chakra to use "spells") and the Binkan clan (based on Star Wars where the clan members had access to the Force and could use it via chakra). Just some examples, we can talk more about Custom Clans later. They also have the ability to submit a 3rd Custom Fighting Style. Everyone else is limited to 2 Custom Fighting Styles.
It's a bit much, but it's pretty straightforward. So what you have is always limited to your rank, same goes for what biographies you can wield. Some require Chunin rank others require Jounin rank, for example. Any questions? (I assume you have some O_O).