if you are applying for citizenship, the first question on the n400 form is:

If you have ever used other names, provide them below

basically here they are asking if you have EVER used another name.

for example, lets say my name is Francisco Diego Lopez but on my drivers license they have it as:

Francisco D Lopez

they i would put it here

IMPORTANT !!!!!! - if you have NEVER used a different name, make sure to write "N/A" in the space for "Family Name (Last Name)."