permitted work, how to report earning and expenses

sergec

hello,

I am receiving ESA suppprt group benefit.
I am about to start doing permitted work as self employed. However, I do not know where to report my earning and expenses. I have looked through google and on the government website, but it only tells you how many hours and how much per week you are allowed to work. There is no information on how to do the actual reporting of income and expenses, whether I have to submit  online, by post or any other way. Does anyone know how it is done.