In Mount & Blade 2: Bannerlord you level up your skills by using them

Mount & Blade II: Bannerlord completely revamps the skill system of the original game, switching from skill points gained on level up to a more Elder Scrolls-style system where you level up abilities by actually using them. Lead designer Armagan Yavuz broke down the details for us at Gamescom. There are eighteen different skills, Yavuz says, and “the player has to exercise each skill individually. If you want to increase one-handed skill, then you have to fight with a one-handed weapon. If you do a lot of trading, and profit from that, the trade skill will increase.” You will make skill choices when you level up, distributing focus points into particular abilities you want to emphasize. “Basically, that doesn't make you automatically learn that skill - you still have to practice that skill in order to learn it - but it determines how fast you're developing in that aspect. So you can say ‘ok, I'm focusing my character on riding,’ for example, or diplomacy, or trade, and then you learn your skills much faster than the other skills.”