set up as a sole trader -yu can do it here
https://www.gov.uk/set-up-sole-trader/register
once you have a business number they will send you a self-assessment tax return each year to fill in -its really easy just basically put in what you've made and how much its cost to make that (expenses)
You can apply for Tax Credits when you are self-employed and yo umay be able to get some sort of grant.
Good luck nailit -remember -where there's muck there's money!