In the Elthos universe characters learn skills over time, most likely by taking classes or getting instruction at the Adventurers Guild. At some point the Character gains enough experience from their adventures so that the Guild registers them as having increased in Level. This is, as far as the Guild is concerned, a designation that they put in their files that allows them to categorize what members have what skills, and their relative proficiency at them. This helps the Guild stay organized, and allows them to assemble adventure groups according to the requirements of given missions. If a mission, according to their estimation, requires a 4th Level Spell Chanter, they have on file which members have the appropriate level to match the requirement. The Guild does this by administering periodic tests. Conceptually the way I think of it is that characters learn skills and are show how to do things. However it is only when they achieve a certain level of confidence (represented in game terms as the Character's Level) can they unlock the skills they learned in a meaningful way to use them with a higher chance of success. This is more about confidence which comes from experience then it is about technical knowledge. So the way this works in the game is that it is assumed that characters who join the guild are learning a variety of skills over time (I do not make the players play out the classroom setting, or the taking of the tests). At some point, after sundry adventures, when they get enough experience and go up in Level, suddenly they get an "aha!" moment and actually "get" how to perform the skills they want to focus on, and therefore their chance to succeed at those skill go up. Mechanically this is a matter of the player picking a new skill to learn. Once they purchase the skill they definitely go up in level at it, but in role playing terms they have only at that point taken a Guild Test for that skill and with their new found confidence achieved that level of mastery.
I hope that's not too hard to understand. If it is, please ask and I'll try to clarify further.