Sloped armor works in the way that if a piece of paper is upright, you can stab through it with a pencil. Slant it slightly and the pencil may bounce off or not go through. This increases the thickness of armor when it is slanted, which is used in every single tank from late WW1 onward. Certain tanks would have very sloped armor to counteract their thin armor, like the Stridsvagn 103, which has an extremely sloped frontal plate that could deflect almost any shell that would hit it. The T-34 was famous for its sloped armor, and German WW2 tasks would almost be useless without experienced crews that knew how to angle their tank property.