Hi, this is a larger criteria as it's what helps you to understand what you do, what's expected of you and how its all underpinned by legal requirements.
There's a thread dedicated to it here:
NOS & job professionalism
If you haven't a job description to guide what you write consider everything you do in the setting from making sure the environment is a safe one for children to be in, to your level of training, how you reflect on things that happen to try and improve outcomes on other occasions, and the knowledge that you have of your early years framework - if in England it'll be
EYFS .
Use a staff handbook if you have one, your copies of the setting's policies & procedures and a level 3 handbook - page 32 of the
preview on amazon.co.uk has some reading for this part.
Best wishes