Player Leveling has its own system of levels.

To improve levels, you need killing mobs.

After killing the mobs you get the message

Screenshot 28

The level progress you can watch in Scoreboard or in Exp BAR

if you have enabled the following function in file Leveling.yml

# Enable/Disable show player level in ExpBar (WARN! This function disable all, what using Minecraft experience)
ExpBar: true

Screenshot 29
Screenshot 30