Before it happens
Pre- comes from Latin prae (in front of, before). With nouns and adjectives it marks something that exists prior to something else: prehistory, precaution, premature. With verbs it means the action happens before another event: preview, predict, prepare, preorder.
Pre- in everyday English
Pre- is extremely common in modern English: preschool, prepay, preorder, pre-existing. When you see pre-, ask yourself "what comes after?" and pre- will tell you what happened just before that thing. The Spanish cognates are nearly identical, making this prefix especially easy for Spanish speakers to learn.