You should only leave the house for very limited purposes. These include
- shopping for basic necessities, for example food and medicine, which must be as infrequent as possible
- one form of exercise a day, for example a run, walk, or cycle - alone or with members of your household
- any medical need, including to donate blood, avoid or escape risk of injury or harm, or to provide care or to help a vulnerable person
- travelling for work purposes, but only where you cannot work from home
The full guidance is here.