basic question need answer

To apply a green card, my approach is PERM/Labor Certificate--->I140--->I485--->? Upon what step I can say I got the so-called greencard?

Is this only one of approaches that lead to green card, if yes, what's special about it?

Upon when I can be free---change employer without any restriction? I picked up from somewhere if I applied green card with this approach, I will stuck with the current employer forever, is that true?

Thanks for any input. This PERM thing has been bothering me for quite some time, I really want to clarify things