Hi romeeeeo,
Rent a room relief is an optional scheme that allows you to receive £7500 in rent each year from a lodger, tax free.
However, this only applies if you rent out furnished accommodation in your own home. If it is a shared property, you can claim £3750 each.
You need to live in the property to receive rent a room allowance.
If the income from your room is above the threshold you will need to complete a Self Assessment tax return.
Further guidance is available at:
Rent a Room Scheme (Self Assessment helpsheet HS223).
Thank you.