The Level of Discipline determine how good your clan is at training and using their Profession.
Professions have Profession Upgrades. Once you reach level 10 in a discipline, you can get a free upgrade of one of the discipline's professions.
There is currently only two or fewer upgrades per profession. The profession and its upgrades often cost resources to train, whereas the discipline costs parchment to train.
Training in the game is limited to one clan at a time, so choose wisely.
You may increase the amount of clans in the tribe, as long as you have the resources for it.