The following documents and procedures are usually required for admission to a university in Spain:

Secondary education: it is necessary to complete your studies at school and get a certificate.
Choosing a university and a specialty: you need to decide on the university and the educational program for which you want to apply.
Application: It is usually necessary to submit an electronic application through the university portal or through the system of access to higher education and vocational education (Sistema de Acceso a la Universidad y a la Formación Profesional, or Solicitud de Acceso).
Entrance tests or exams: Some universities require entrance tests or national exams, such as the Prueba de Acceso a la Universidad (PAAU) or Selectividad. In other cases, the university may consider grades for secondary education.
Grades and academic performance: it is important to have good academic performance at school, as the competitive struggle for admission to university in Spain can be high.
Other documents: documents such as a copy of your passport or ID card, photos, resume, statements of consent to data processing, etc. may be required.
It is important to note that the application procedure and requirements may vary depending on the university and the chosen field of study. Therefore, it is recommended to contact the university or the official website of the university to get detailed information about the admission requirements and rules.