I (American) am going to study a masters degree in Spain, need helpp

I just got accepted into a masters programme, and I would like some help/advice. All the need from me before July is an "equivalence degree document" (something I think I do through a Spanish government website), and an "apostile" and legal authentication of my US diploma sent to them. How long do you think this may take? What do I need to know? I feel a bit lost but it's been a dream of mine to study in Spain. Thank you!