x86 gives instructions which allow for manipulating memory as a stack.
This is useful allocate memory statically, in particular to allow function call recursion.
The idea that when you enter a function you store the top of the stack in ebp and do no change ebp inside the function, only when leaving it.
This way, the first variable will always be at ebp - 4,u even if you allocate more data on stack for local variables, moving esp
If this were not done, allocating data would move esp, and the position of arguments would depend on how much data was allocated, much more complicated to implement.
Then, when you leave the function, you restore esp and ebp, deallocating the local memory.