You have been advised to stay at home. Anyone with symptoms should stay at home for 7 days. If you live with other people, they should stay at home for 14 days. After 14 days, anyone you live with who does not have symptoms can return to their normal routine. Please read the following guidance.
Here's the NHS COVID-19 advice. It gives information on staying at home, avoiding the illness and other useful tips. https://www.nhs.uk/conditions/coronavirus-covid-19/
Covid-19 and sick notes
Coronavirus Sick Note Request Letter