What is First Three Instructions in the Disassembled Code

Question

What is the meaning of the first three commands being the same after most programs are disassembled? What is the meaning of the first three commands being the same after most programs are disassembled?

For example, below you can see the disassembled code of exe:

push ebp
mov ebp, esp
push -1

Or when I disassemble another exe, it looks like the following:

push ebp
mov ebp, esp
sub esp, 0x3f4