The city government takes care of the paper work, everyone needs one to get essential services in Spain and it has to be renewed every year or so. (The site below specifies expats, but everyone needs one)

Here is some more information:

https://www.thinkspain.com/information/moving-to-spain/what-is-the-padron-and-how-to-register-on-it

From that site:

If you are an expat living in Spain, it’s important to get registered with your local town hall on the padrón.The Padrón is essentially a register of the local population of a town or city in Spain. In Spanish it’s full name is Certificado de Empadronamiento. It is the certificate that confirms your address, your connection with the town/city, and your official residency in that area. This register allows the town hall to track the population and calculate the resources that should be allocated.

Where I live in Spain this is exactly the case, it’s called a Padrón, and pretty much everyone adheres to it. Without it it’s impossible to do most any business in Spain.