Instructions
Check your inventory. If you do not have enough free space in your inventory you will not be able to pick up any loot.
Enter a battle. You can only loot your enemies during a battle.
Defeat a normal enemy. Most of the time, they will simply die. However, occasionally, an orange "Finish!" icon will appear above them. This means you have the opportunity to finish them off and get access to their evil core.
Move over to the fallen enemy and click the right mouse button. This will "finish" them. A yellow "Get!" icon will appear above them.
Move to the "Get!" icon. You will see a small ball of black smoke. This is their evil core; press the "Grab" button (by default it's the "E" key) to pick it up. A new item will be added to your inventory.
Defeat a boss monster during battle. Unlike regular monsters, you will not have to "finish" the boss monster in order to loot them. Furthermore, boss monsters always drop loot.