I'm new to assembly language and my faculty gave an assignment which I cannot figure out how to do. Please help me understand the code....

The assignment as follows: Take 4 digits from user as string(alphanumeric to integer), convert them into a number and store in AX

if user input is '1','2','3','4'
the output should be: 1234

P.S. I don't want the code, I'm having trouble understanding the procedure