He wrote the story with his friend's 'assistance'. = He wrote the story 'with the assistance of' his friend. [=his friend helped him to write the story]
Our family had to 'go on public assistance' [=receive money from the government] when my parents lost their jobs.
Nobody 'came to her assistance' [=nobody helped her] when her car broke down.
(..) – Then play him that way, give me your black slaver. MOGUY: Dr. Schultz! Good to see you again. – Mr. Moguy. Thank you for your assistance in creating the opportunity for this appointment. – Nonsense, it's my job. So, this is the One-Eyed Charlie I've heard so much about. (..)2012 Django Unchained