Use cursor keys or w,a,s,d to move. Press space bar to access the menu screen and pause the game. Keys and hot-keys can be redefined from there.
Default bindings for hot-keys are E:exit the level, F:shoot/throw current weapon, Z:search for traps, X:disarm trap, C:summon minion
Run into monsters to attack, or jump on their heads to knockback-stun them.
Press up to pick up loot.
Equip yourself and your minion with loot from the inventory menu.
Use magic by exploring the options available with runes you collect in your inventory menu. Runes have different effects on different things - it's up to you to figure it out.