How to enter the protected mode of the processor?

Question

assembler

Good day, users !
Need practical help on the issue of the protected mode of the processor. How can you enter it, do any action (the simplest that can be, purely for an example) and exit without errors.
Thank you for your responsiveness!

Answer 1

Entering protected mode:

mov eax,cr0
or al,1
mov cr0,eax

We do "any action (the simplest that can be, purely for an example)" , read the contents of the eax register into the ebx register :
mov ebx,eax
Exit protected mode:

mov eax,cr0
and al,0feh
mov cr0,eax

And what? Why is this?