I would know in wich way can I configure SP in a determinate point of memory

For example

Cseg

org 0000h ;program starts here

and now for SP???

I have seen pices of code like:

Cseg

cseg

org 0000h
ljmp start

org 0100h ;is this for SP?

start: ..........

Is this correct? can you help me?

But with only -org 0100h- in wich way the mC understand wich is the SP?

Thanks

org 0100h