To cast a spell you need a staff. You can either find a staff on a monster, or buy Runescape Gold from an NPC vendor.
Most active skills in Dark-fall follow the load and fire principle. You select the skill of spell you want to perform (drag the ones you use more often to the hot-bar for convenience), then press the LEFT mouse-button to perform the action.
You can't loot a target with your weapon drawn. When monster or players die, they leave a tombstone which can be looted by pressing the use key. When the loot box opens, this will put you into UI mode, so you will not be able to move or do anything. You also need to open your backpack (Default "B" button) and manually drag and drop the items from their corpse to your bag one at a time.
This will definitely be perceived by many as clunky, but at the same time there is a case to be made by others that looting should not be fast to prevent people from cleaning out bodies quickly in the middle of a heated battle.
After playing for a while, I think it has grown on me a lot because the time associated with cleaning someone out adds a risk when you are in a heated situation.