3. What details do I need to fill in?

Name, email, a contact phone number (required — it's the only way to reach you quickly if there's a delivery issue, for us and for the carrier), your shipping address, and your NIF/NIE/CIF for the invoice. The name you enter is also used as the recipient's name. If you need to bill a different address than the shipping one, there's an option to set that in the same step, without filling everything in twice.