Move your character near the enemy and press Q for a quick attack. As you strike the enemy, press SPACE. The attack menu will appear again, allowing another attack. Repeat this until your enemy has been killed.
If you take Krevish (the NPC you first save in the game), you will make him a lackey. Usually you cannot get anything from a NPC once they have it, however if you go to any of the vaults, highlight his name and click "Deposit". You can get money or items from him.