When a general fights battles or an agent carries out their mission they gain experience. With enough experience behind them they will increase in rank and skill points will be issued. At this stage they may invest a skill point towards acquiring a new skill or upgrading an existing one, allowing you to shape a character's career path. Skills require one point per upgrade and one point before they are awarded. Certain skills are associated with specific ranks, meaning that they cannot be acquired until the character has reached that skill’s rank requirement. The skill tree can be viewed via the character index at the top of all encyclopaedia pages.
As a general gains experience by leading your armies into battle, his rank and skills develop across three distinct disciplines. The "Commander" develops his influence over his troops in battle, improving his ability to inspire and rally them. The "Strategist" develops across a campaign by reducing recruitment costs, speeding-up unit replenishment, and increasing army movement extents. The "Warrior" has influence on both the battle and campaign maps, using his growing reputation to improve unit abilities and reduce the enemy’s morale on the battlefield, whilst increasing happiness throughout friendly regions and provinces. Your general can progress evenly in each discipline or choose to specialise in a single area.
The skill tree is where the experience gained by characters during a campaign can be used to acquire useful skills. Many skills also have several levels - each with increased effects - so it is possible to use experience to increase the level of a chosen skill, as opposed to selecting an entirely new one.