Why does the earth on its axis causes summer to be warmer than winter in the northern hemisphere?

not sure if this is what you mean but:
the earth tilts up during winter when facing the sun so it gets less direct sunlight
during summer it tilts downward toward the sun so it gets more direct sunlight
example:
if you take a ball and shine a light on it the upper part gets less light because it is spread out but in the middle it gets direct light so it is getting warmer