How do foreigners apply to Universities in Spain?

hi! I'm currently living in the US I'm a high school student, planning on moving to Spain soon, for University.
how would I go about applying for a Spanish university?
besides visas (I have European citizenship, don't need any) what else would I need in the application process?
as of transferring transcripts and making sure my US high school diploma is equal to that of a Spanish high school diploma, how do they check for that?
( I have a 3.5 GPA, and take pretty average electives) if my diploma is not equal to a  Spanish high school diploma, how would I go about making it equal?
what is the average acceptance rate in universities in Spain?
and lastly what is the raw tuition for a semester or year in a university in Spain? (preferably Universidad de Sevilla and Universidad de Malaga)
thank you :-)