[Lance doesn't at all mind these questions, in fact he's rather happy that someone is so interested. While people have asked him questions before, Luke has been the most interested and enthusiastic.]
There is no simple way to answer that. Pokemon battles stem from a Pokemon's natural desire to fight. Battles are how a Pokemon grows and matures, both physically and mentally. As they gain more experience, they learn new attacks and increase in strength. It's built into them and is part of their nature. The same can be said of trainers really. Many trainers start as young as 10 years old, and go on a journey around their respective region challenging other trainers. The Pokemon League manages this by providing eight gym leaders for trainers to challenge in different cities around a region. If a trainer defeats a Gym Leader, they earn a badge. After earning all eight badges, that trainer is allowed to challenge a region's Elite Four, and ultimately the champion for the title of champion themselves.
[Action]
There is no simple way to answer that. Pokemon battles stem from a Pokemon's natural desire to fight. Battles are how a Pokemon grows and matures, both physically and mentally. As they gain more experience, they learn new attacks and increase in strength. It's built into them and is part of their nature. The same can be said of trainers really. Many trainers start as young as 10 years old, and go on a journey around their respective region challenging other trainers. The Pokemon League manages this by providing eight gym leaders for trainers to challenge in different cities around a region. If a trainer defeats a Gym Leader, they earn a badge. After earning all eight badges, that trainer is allowed to challenge a region's Elite Four, and ultimately the champion for the title of champion themselves.