The entirety of the game is focused around a central town. The town is divided into separate regions with a general level range for each section. Players can gather at the region near their level and try to obtain a party there. The problem with this is that players can become heavily clustered making it difficult to find players that you are looking for or to click on them to form a group.
From that town, you can enter certain parts of the map to trigger dungeon areas. Each dungeon is instanced for each group of players. Each dungeon is further divided into difficulties. The higher difficulties unlock when the previous difficulty is completed.
The difficulty goes
Skill experience rewards the player with skill points when it fills up. There are also rare items that will boost a players stats and skill points but they are one time rewards from some of the quest chains. They may not seem like much but over several quest chains they can add up to many stat points.