How are buffer overflows used to exploit computers?

Question

How are buffer overflows used to exploit computers?

How is one able to execute arbitrary code simply by causing stack or heap overflows?

I understand that

Answer 1

The stack contains both data and return address when you jump into a subroutine. If you manage to put a specific address on the stack where the return address is, you can force the CPU to jump to a particular memory location, the one where y ou put your own code. That's for buffer overflows. Heap overflows is a bit different and more difficult to exploit.

Stack overflows are just indication that you've run out of stack space (which is generally more limited, especially in the kernel).