I need assistance with NASM assembly language, please help me with the following questions.

Instructor Question 3: Why do we do this; i.e. adding 0 to the number? What is the purpose of this? add eax, '0'

Instructor Question 4: What are we doing here?

mov eax, 4 ; System call number (sys_write) mov ebx, 1 ; File descriptor (stdout) mov ecx, edi ; Address of the message to write mov edx, esi ; Message length int 0x80 ; Call the kernel

Please give me any help that can be given I am not too familiar with this topic.