Eu citizenship

There are plenty of threads on here about applying for residency. You cannot get citizenship until you have been a resident for 10 years or more, pass a written test on Spanish history and current affairs, attend a 30 minute interview conducted in Spanish and show that you have integrated into the Spanish lifestyle. You would then need to rescind your current nationality and swear allegiance to the King of Spain and give up your current passport.

Applying for residency must be done at a Spanish consulate in your home country, showing a minimum income of €28,000 per year plus private medical insurance. You are not allowed to work in Spain for the first year.

Alternatively, you can get a work permit but that requires a guaranteed job offer with a contract and the employer must show the work cannot be carried out by another EU citizen. Unless you have a much needed qualification - such as medical research, high end IT skills, engineering experience etc - then you need the job offer.

You can apply for a golden visa which means purchasing property, or properties, valued over 500,000 euro not including taxes, investing in Spanish companies for over a million euro or investing in Spanish bonds at a value exceeding 2 million euro.

There is a digital nomad visa which means working online for a company not based in Spain (and doing no more than 12% of its business with Spanish companies) but would still have to prove a minimum income of €28,800 per year and have medical insurance

As said, look under the help and advice sections on residency to get the full procedures.