The Player Level is a progression feature which was introduced with Patch 2.0.0.

Leveling up the Player Level will award the Player with a certain amount of Iridescent Shards, depending on the Level reached, which can be spend later on Characters Customization/Outfits, Survivors, Killers or Perks in Shrine of Secrets

Experience Points or XP are needed to level up your Account Level.
They are obtained after each trial and are calculated depending on the following factors:

-Time played in the trial
-Highest Emblem Quality

• 18 XP for obtaining at least 1 Iridescent Emblem
  
• 12 XP for obtaining at least 1 Gold Emblem
  
• 6 XP for obtaining at least 1 Silver Emblem

There is also a "First Game of the Day" bonus (300 XP), that can be obtained for either side for completing the first trial of the day.

Passing Level 99 will reset your level progress back to Level 1 and give you a Devotion Level.

Devotion can be taken as some form of "Prestige" or "Paragon" levels, and there might be some rewards coming up for it.