Writing an OS kernel in assembly with NASM

Question

I want to know what is the standard way for writing a -simple- kernel to be compiled on NASM?

To get it clearer: I was able to define the code block with all the following ways:

[segment code]
[segment .code]
segment code
segment .code

[section code]
[section .code]
section code
section .code

I need to know what is the standard way to do that, And what is the difference between them...

Thanks