How does graphic affect performances?

I’m trying to understand how the graphic rendering affect the game performance. I can’t find numbers. So could we compare the drawing of a square to a regular event with numbers?
For example, let’s take the drawing of a 10x10 pixels square at different position at each frame. This would be equivalent to how many regular events (checking the value of a number variable and affecting new number to a variable)?
Maybe it depends on the graphic card. In this case what would be the answer for a computer with a very low level graphic card and then for a middle level one. I hope this question makes sense. Thank you