Whenever you do something summarily, you act without hesitating or even taking time to explain yourself. A strict babysitter might announce, "Bedtime!" and summarily flip off the lights and close the bedroom door.
The adverb summarily describes things that are done in an abrupt, brief way, without any extra details. It's kind to explain to a job applicant why you're not hiring them, rather than summarily saying, "There's the door, goodbye." A related word is summary, meaning "brief," or "containing just the sum or substance." The Latin root, summa, means "whole or gist."