Every drone operator is obliged to register drones that weigh more than 250 g or carry a camera or other sensor capable of capturing personal data in any way. It is not the individual drone that is registered, but its operator (usually the drone owner). For operators under 18 years of age, the registration must be done on their behalf by their legal representative. You can register online through the Civil Aviation Authority's website. A list of country's registration page can be found here: https://www.easa.europa.eu/domains/civil-drones/naa. All drone pilots, except those flying very light C0-rated drones, must also undergo mandatory training and pass an online theoretical knowledge exam. The registration number obtained must be marked on each drone of the operator subject to registration. All further information can be found on the following website: https://www.easa.europa.eu/domains/civil-drones-rpas