"을/를 의해(서) and 에게/한데/게" 을/를 is the object particle. It is used by itself, not with 의해서 (e.g. 영화를 보았다). 의해(서) is used in the -에 의해서 form. It indicates an agent of action that brought about some effect or results (아이작 뉴턴은 지구가 당기는 힘에 의해(서) 물체가 땅으로 떨어진다는 만유인력의 존재를 발견했다). 에게 and 한테 are like "to" in English (친구에게/한테 전화를 했다). It is only used for people or animals (for inanimate things, 에 is used). 게 doesn't exist, but there is 께. 께 is the same as 에게/한테 except that it is a respectful word only used for people older or higher in stature (선생님께 전화를 했다).