sometimes after hunting monsters, you may find precious money or even expensive items.
These spoils of war all yours to keep as a reward of a victory.
These items can be exchanged with game-money from the merchants, which then you can spend these money on better weapons and armors, potions or learn new skills.
To see the belongings of dead monsters, you can either double click on the corpse or press F when the corpse is targeted. You get to keep all the treasures.
You can drag the items from the window into your bag, double click on the item or you can press the little buttons on the bottom of the window to make them yours.
Easiest way to bring all the treasures into your bag at once is by pressing Z button on the keyboard.