PvE — Player vs Environment. To the PvE focused players the primary challenge comes from tough mobs like instance bosses rather than other player characters.
The PvE mode contain a storyline that is narrated as the player progresses through missions, Daily Portal for farming resources, Trials where you can get elite creatures and resources and Raids available by creating/joining a guild.
Daily Quests may contain a quest to clear a PvE stages on a specific difficulty. For completing a lots of PvE stages on "Normal" or "Heroic" difficulty you get an elite creatures. And for completing on "Champion" difficulty you get gems.