Assistance
Support, Assistant
noun, verbal noun, の adjective
A supplement of help is a form of assistance.
補佐 is a formal word for the act of providing support to a leader or person in charge. It can also refer to an official or organizational role, like 部長補佐 (an assistant general manager).
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
私はトーフグ営業部の補佐として働きました。
I worked as an assistant in the Tofugu sales department.