Летать vs лететь is not important. "лететь" is about single event, "летать" is more like "present indefinite". maybe multiple times, maybe one time, indefinite.
But the key idea is that perfect verbs can be divided by two groups: "(start and) complete event" and "start event" (if you mean by "event" meaning of imperfect form). I think you should look at vocabulary, because I do not know exact rules to distinguish these cases by prefixes or suffixes.