For the most part, League of Legends players can get their desired champion skin by using RP to purchase them from the store. During events, players can grind through missions to redeem their points for the limited-time prestige skin, or they can be used to buy Mythic Essence, which can be used to buy skins that rotate regularly.
In all, there are hundreds of League skins for players to enjoy, though some carry heftier price tags than others.