Peasent:You start as it
Warrior:Must earn the title from hard work for your nation/tribe leader.Also must have at least 150 posts
Guardian:Must Be a skilled fighter.You must be told by the Nation/Tribe Leader that you will protect their nation.But, you have to fight a Guardian from the same nation and pass the test.Must have at least 300 posts
Captain:These are mostly captains of ships for a Nation/Tribe.They can also be like leutentants.At leasts 450 posts
Master/Lord:The highest rank.They get the most respect.You must be a Tribe/Nation Leader or become a Bending Master of an element.You Become a Bending Master when your tribe/Nation Leader tells you.
Only Bending Masters may teach other people how to bend specific elements.But if you just need fighting or weapon training you must be Captain+ to be a sensei.