This mechanic makes players have to constantly repeat something so that It is improved. This can be done in skills, use of weapons, etc. This is commonly used in role-playing and online games.
A good example a game that uses this mechanic is Runescape. In order for the player to level up, their character they must first level up a range of fighting skills. These are Attack, Strength, and Defense. To level these skills up the player must fight a certain amount of monsters until it eventually levels up. After leveling them all up a certain amount of times it then levels up the player. In turn giving them rewards.
Another example of a game that uses this is Elder Scrolls Skyrim. Depending on the type of weapon the player uses determines what skill they are ranking up. By continuously killing enemies with that weapon it will level up and give the player a choice of perks that they can unlock.
If I was to use this mechanic in my own game It would be like in Skyrim. The player makes progress through a skill depending on what weapon they are using and by repeating a task of killing a certain number of enemies.