Oral consecutive translations: always when translator is needed. Oral translations include e.g. business meetings, ceremony of entering into a marriage. First, translator listens to a fragment of text and then translates it.
Oral simultaneous translation: during this kind of translation, both speaker and translator speak at the same time. This type of translation is very common during international meetings, lectures, conferences etc. Variants of the simultaneous translation include cabin or whispering translations.